When people say "something lacks answers", it is not about the raw number of things that can be an answer to something, but moreso how reasonable would it be to include said answers in every team - since you always want some ways to deal with each relevant threat in the metagame - while having an overall functioning team. For example, if there is a pokemon (let's call it Charles) that beats every team except the ones including an LC Pokemon, it still would be broken. Sure, there are a lot of LC Pokemon and thus Charles' answers, but would it be reasonable to include one LC Pokemon in each team? No, because LC Pokemon are just awfully outclassed by fully evolved Pokemon in any other matchup.
In addition to this, if for example Charles not only loses to LC Pokemon but also loses to a good pokemon such as Heatran (But still 6-0es the rest of the metagame), it would still be not worth running because it is not reasonable to ask every team to either bring Heatran or an LC Pokemon.
Smogon wants to put emphasis on the playing skills, and if a Pokemon impact on the metagame basically is "I win unless the opponent brings one of the otherwise garbage/ultraspecific Pokemon that beats me" (So effectively removing the relevance of each players in-battling skills), it probably is not worth keeping around. Ban Charles imo.
The answers you have listed are too specific to be fit on every team, are not enough to stop Barraskewda as a whole, or are just not worth to run in general.
-Changing weather is something restricted to weather teams, and you can't assume you'll be able to reset the weather all the time, as Rain teams are very offensive, and getting a free turn against them is not always possible. Furthermore, you still have to find a way to check Barrask even when Rain isn't up, as it still a threatening Pokemon on its own right.
-Unburden+Terrain is not something you can fit on every team either, and is not sufficent counterplay either: Hawlucha can only revenge kill once. Barraskewda can just switch out, and unless Hawlucha wins immediately Barraskewda will just win later in the game if that was your only way to deal with it.
-Trick room is not only restricted to a very specific kind of team built around the move, but also has a greater overall issue: Trick Room can't be up at all times, and you need a free turn to set it up. Sure, Barrask will not be a threat while Trick Room is up, but what are you going to do during the turns it is not up?
-Immunities is a quite valid point, but has two main issues:
There is only two mons that are good mons worth to run aside from being water immunities : Gastrodon and Clodsire, that aren't even that great at switching into it since physically defensive sets still can be 2HKOed by Close Combat or Drill Run respectively (252+ Atk Choice Band Barraskewda Close Combat vs. 252 HP / 252+ Def Gastrodon: 189-223 (44.3 - 52.3%) -- 17.6% chance to 2HKO, 252+ Atk Choice Band Barraskewda Drill Run vs. 252 HP / 252+ Def Clodsire: 272-322 (58.6 - 69.3%) -- guaranteed 2HKO). Furthermore, Rain always bring Ferrothorn, so even if you manage to check Barraskewda with a water immunity, Ferro is just going to take advantage of them and set hazards.
-Focus-Sash + Endeavor is completely invalidated hazards, something pretty much every team run due to how good they are. They also can directly go on Ferrothorn to break your sash, as Endeavor is a contact move, or just click Flip Turn on barrask if this is an 1v1 situation. Counterplay should almost always take Hazards into account, as you can't assume being able to keep them off at all times, especially since removing them (if you get the opportunity to - which is not guaranteed at all) essentially gives a free turn to the opponent, which they can take advantage of to break through your team.
-Priority is
kinda valid if we assume that chipping the fish would be enough to deal with it (which is not the case!), though Barrask resists some of them (Ice Shard/BPunch), however you will have to ensure that your priority user is a threat in general to rain otherwise you are just losing. Imagine if you brought M-Scizor, sack something to let M-Sciz safely get into the field, just for it to give a free switch to something like Zapdos that threaten to get an other kill, can you really say that you have enough counterplay to Barraskewda?
-There are bulky stuff that can somewhat switch into Barraskewda to take its hits, but that's the whole deal with Tera water: It hits so hard that you will have to be a bulky resist such as Toxapex and Ferrothorn to take the hit comfortably, and you will have to take into account the fact that Barraskewda can keep the momentum against them with Flip Turn if those are the only counterplay you brought to it, restricting your build options even further.
-Lele can only revenge kill if it has a scarf, and has to win the FocusBlast/Moonblast vs Tera mindgame. Otherwise you could sack Lele to get terrain up but then you still need something able to revenge kill it at +1.
-About the ghost/steel/rock types : You def should give concrete examples instead of generic categories : there is a lot of bulky ghost/steel/rock types, but not all of them are really worth putting into teams. Also they need to be able to do something back to dragonite as well - which is not guaranteed, as dnite still is pretty bulky and has multiscale.
-Boots exist + Hazards do not OHKO Dragonite as well. Yeah sure they help, but you can't always assume you are going to have them up + they are obviously not enough. This is true with anything weak to rocks - not exactly on topic, but
this video about protect ho-oh in dpp Ubers illustrates how ho-oh manages can be an immense threat in a metagame where removing rocks is pretty much impossible.
-I already went over sash.
TLDR:
Generally, making a list of stuff that beats a Pokemon is NOT a sufficient argument, otherwise you could argue that absolutely anything is worth unbanning. For example, i could go like:
Hey guys, we should unban Primal Groudon from natdex OU because there is a lot of counterplay to it! Like:
-Any faster ground type threaten it with ground moves (Landorus-T, Iron Treads, Garchomp, Great Tusk, etc...)
-Lati twins wall most of its sets, and outspeed it
-Any set lacking fire moves is dealt with by steels immune to ground (corv, skarm, bronzong, celesteela, orthworm (lol)).
-It is very slow, a lot can outspeed it and kill it once chipped, especially since it is much less bulky specially speaking.
-Neutral to rocks and has no recovery, so probably quite easy to chip
-Focus Sash (or anything bulky enough to take a hit) + Counter
-Solrock and Lunatone resist its stab combination, and wall any set without toxic/solarbeam/SD
-Ditto can revenge kill any set
-Golduck is faster and can kill it with a water move since it ignores Desolate Land
-...
This is fucking Primal Groudon though. Every single thing in the game has multiple counterplay options, but what matters in the end is : are those options really reliable enough? And if they are, is it reasonable to fit one of these options in every team? What if those options make my team significantly worse in other MUs?
