I think that a lot of people are going to sort of instantly assume that it should be banned and that this will be a very lopsided suspect, but I honestly find Meloetta to be a lot closer of a call than most. At the end of the day, I do, indeed, find that the tier lacks the defensive counterplay to sufficiently deal with Meloetta on a consistent basis, but I think that a lot of people either are lazy in building or do not approach things properly in general when trying to prepare for Meloetta, so I would like to give my genuine, open minded opinion on the subject as a whole instead of just giving my eventual, hardly convinced pro-ban vote after I get my reqs in a few days. To do this in the correct fashion, I think it is first best to break down Meloetta in the context of the metagame -- showing what it can do, what can defensively check/counter it, and what can offensively check it. After all of this is out on the table, drawing a conclusion becomes relatively straightforward after all.
To start, Meloetta can run a plethora of sets and there is no denying this. However, the main variants of Meloetta that should be discussed in this thread, in my opinion, are the Choice Specs and Colbur + Three Attacks variants of Meloetta. While there are some less consistently seen and more niche sets such as Relic Song mixed, Substitute + Calm Mind, various Z Moves, and Choice Scarf, I find all of these to pale in comparison to the aforementioned Specs and Colbur sets as they are more reliant upon set-up/support, less immediately threatening, and/or simply countered by a wider array of viable Pokemon throughout the metagame.
The Choice Specs variant is definitely the hardest to switch-in to and counter, but it also has some downsides and we must take these into consideration when trying to figure out if Meloetta is truly banworthy or
not. I think that a glaring communal misconception that I find coming up time after time in suspect discussions and metagame discussions is that a Pokemon being able to 2HKO the entire (or almost all of it) metagame does not necessarily have to be broken. It obviously can be indicative of a banworthy Pokemon and I'd even go as far as saying that this is the case more often than not, but there is no surefire causation based relationship between the two. An example of a Pokemon that can 2HKO the entire metagame (outside of Uxie, Weezing, and Tangela) is Choice Banded Mudsdale. Needless to say, this Pokemon is nowhere near broken and it is only fringe viable, but it can still 2HKO everything if locked into the right move. Choice Specs Meloetta also happens to fit in this rough category, but it happens to (obviously) have many more things going for it than the aforementioned Mudsdale and it also happens to be much less forgiving when it comes to how good it is in a practical sense right now. The whole point I made about 2HKOing everything is to hopefully rid this thread of arguments such as "Specs Hyper Voice + Psychic + Focus Blast 2HKOs everything, so Meloetta should be banned" as that, in itself, is not a fully sufficient pro-ban argument, in my opinion, but it is only the start of it.
You have to really make a practical extension to this to make a complete argument. Let's go back to the Mudsdale comparison once more so I can explain what I mean by this -- sure, Mudsdale can 2HKO everything, but if it locks into Choice Banded Earthquake and does 55 to Slowbro or it locks into Choice Banded Rock Slide and does 55 to Golbat, then it is not necessarily making much, if any, long term progress. Think about it -- in the former scenario, Slowbro can switch out into a non-grounded Pokemon consequence free or stay in whereas you can stay in and Earthquake again or double-switch out predicting him to go to his immunity, opening up a lane for competitive play, where the player who made the better move ends up in the better position at the end of the sequence. As for the latter, Golbat simply roosts it off and the practical point comes into play as you can be as strong as anything in the world, but if you lack the Speed or general practical traits to thrive in the metagame, then it doesn't mean much in practice at all. On the contrary, if you look at Meloetta's Choice Specs set, you notice that it has an above average Speed tier in the metagame, it does not have many things that appreciate taking its STABs from the Specs set even if it is resisted, and, if played properly, it can almost always pick-off a Pokemon or force a scenario where it can come out making significant progress. Meloetta is a Pokemon that is suited very well to take advantage of the strength to practically 2HKO the entire metagame and that is why I believe the Choice Specs set is likely too much for the metagame to handle.
With this said, you do have to consider the downsides of Meloetta's Choice Specs variant -- there is sufficient offensive counterplay to it in the tier, in my opinion, given that it does not have the best (not too poor my any means) natural physical bulk, it is vulnerable to Pursuit, and many offensive teams have 2-3+ Pokemon that can outrun it. With this said, many teams have at least a defensive backbone and bulkier teams lack the offensive presences mentioned above more often than not and this is where Meloetta truly stands out as a broken presence as it can pick things apart if it clicks the right move or at least generate momentum to the extent that any well-built team has the tools to break through without a ton of outplaying. Another downside of it is that Specs Meloetta does have to lock into a move each time it comes in when the tier does have Regenerator defensive pivots like Slowking and each of the moves it finds itself clicking have a lot of individual immunities or resistances, making the potential progress it would make in those situations much less noteworthy than otherwise and leaving the situation in the hands of taking advantage of chipping things and predicting potential follow-ups or not, which is arguably a healthy sequence that leads to the better player coming out on top. Unfortunately, this is not exactly the most universally applicable logic and you cannot put too much emphasis on this argument as Slowking does still get 2HKOd itself, it is only one Pokemon in the metagame, and there are not many others that can situationally check it to the same extent. With all of this taken into consideration, I think that it is fair to say that the power and convenience of Specs Meloetta in the context of the SM NU metagame is a bit too much for the tier to defensively handle without limiting teambuilding and gameplay to a greater extent than deemed acceptable, in my opinion, but it is by no means broken solely on the basis of how it can 2HKO everything and it is not even overwhelmingly broken, so I do hope that people give it the fair consideration it is due.
Onto the Calm Mind + Three Attacks Colbur variant! I'd say that this set plays quite a bit differently than Choice Specs, but I think that the end result in terms of our discussion here is quite similar. I mean, sure it lacks the immediate power, but Meloetta still attracts the same defensive checks/pivots (note that I did not use the word Counter as there really aren't any although given that CM does not run Dazzling Gleam, the rare Sableye and Spiritomb do suffice), gets a relatively easy Calm Mind up against most of them, and then poses an even larger threat with the cost of letting the opponent potentially make a ballsy prediction to pivot into a faster Pokemon predicting a resisted attack or Calm Mind or try and do whatever damage they can to you with their supportive Pokemon (generally, a status move or a relatively weak attack that fails to 2HKO).
I find that the presence of the Choice Specs actually compliments the Calm Mind set quite well given the above scenario that I alluded to, but that does not mean that it is just easy pickings for Meloetta as it is easily revenge killed, even with Colbur Berry. Colbur does making trapping it much more of a challenge, however, granting it an element of greatly appreciated longevity in some match-ups. Ultimately, I feel like this set is not even a traditional win condition that sweeps teams at some ungodly rate that some people might think it is when they associate "broken" and "CM Meloetta" in the SM NU metagame, but it is an awfully good hole-puncher during the mid-game stages and I feel like it's almost always coming away with a kill in the long run unless the opponent makes high-risk plays around it consistently, which is arguably not healthy for any individual Pokemon to singlehandedly do.
Given this, I find that the Calm Mind set is probably a bit less of a pressing issue than the Choice Specs set if only because of the lack of immediate power, but it also probably has a higher ceiling in the right match-ups as it can shred through cores and if the revenge killer is not suited to kill a Colbur Meloetta, then it still can function as a win condition or simply do too much to a team for it to realistically come back in a game. I'd definitely group this in there as a controversial set and I think that Colbur CM Meloetta contributes to it being somewhat broken in the metagame, even if it does not necessarily do it alone.
Ban Meloetta