I think you missed the point, I can make Landorus-I timid if you want (ill do less damage sure), the point still stands: Latios is a poor answer to Landorus-I, as its basically forced to use Surf, and if it actually gets a KO, then Tyranitar is trapping it (or Tyranitar can run Scarf and switch in not giving a fuck). You say "Many things in the OP can take a hit" but really, I pretty much see Celebi, Latias, Jellicent, Rotom-W and Gengar (everything else gets risky as fuck if SR + SS is up) from listed in the OP (I might have missed the odd thing but thats what stood out). That is not "many things" especially when 4 of them are Pursuit bait.
Now don't get me wrong, Landorus-I is not uncounterable / uncheckable, it has mons that can take a hit from it etc etc, the point I was trying to make is that Tyranitar can checkmate many of them, which makes them exceptionally hard to bring in. You see, when you bring in Specs Latios on a Landorus-I after its smacked you with an HP Ice, or if you have taken prior / residual damage or whatever, you want to even out the trade, you want to deal damage, however Tyranitar puts you in a nasty position because IF you get a KO, then you get trapped, and its 1 less obstacle to Landorus-I. Sure, you can double up on checks / counters (sorta proving my point but w.e) and Landorus-I can do the same, running lures or mons that overload its counters and around and around it goes.
I actually invite you to read kd24's
post a few pages back, it had a similar situation you might enjoy. Basically, he had a Keldeo in against a Hippowdon, so the chap switched in Latias, taking the attack with ease. kd24 then stayed in with Latias, knowing if Latias attacked and defeated Keldeo, Tyrantiar would trap it, and Landorus-I would rain hell on the team (despite it having a secondary check in Jellicent), sure enough Latias switched right back out to Hippowdon (to counter the Tar switch in) and Hippowdon was slammed with a Hydro Pump, and basically that was the game.
Now obviously there are a few slightly differences since it was Keldeo being the aggressor but it illustrates my point, against Landorus, bringing in your counter / check is very risky when it is so easy to pay for it with Tyranitar waiting in the wings. If you don't like these "team arguments", then feel free to post 1 or 2 more mons of your own (Latios + ???) to your core (its commonly accepted that Tar / Keldeo / Landorus-I is the common 3 mon core that's getting discussed, but Tar / Landorus-I works just as well), instead of complaining!
Quoting so you see it
So Landorus cannot come in and sweep now because odds are, I probably have something else that can tank a hit form Landorus.
Please mention this "mystery mon" because nothing is more irritating at having to argue against a scenario, when that person suddenly adds an unnamed mon (Iv been open with the partners iv been using so I don't think im guilty of? (if so sorry but I think iv been careful)), Just tell us your core, and we can judge for ourselves if your argument holds true, because most things cannot switch into CB Tar / RP Landorus-I and its pretty difficult :/
IRL, my opponent would have to guess which of these "counters" I'd bring and choose the appropriate attack.
Its called Team Preview, and it lets me see exactly what mons you have that can go toe to toe with Landorus-I, lets me make justified calls such as HP Icing a switch, what move is best to use etc etc. Don't act like doing the above is so hard, team preview makes things much easier for players of any skill level to do. With team preview I can see, ok so I need SR here, a Latios trapped HERE, the enemy Keldeo using SS HERE so Landorus-I can sweep and that's my gameplan. It doesn't mean ill auto win the game by any means, but I can instantly see what checks + counters you have, so I can justify using RP (against balance I can often attack w/o boosting first) or something else and so on and so forth.
The problem for most of these arguments is the pokemon attacking Lando is in a vacuum while Lando itself has a team built around it.
This is a fair argument, its been discussed a fair bit and its an issue I guess. I don't think people are really mentioning a team tho, its usually Landorus-I + Keldeo + Tar, or Landorus-I + Tar. The point is, talking about Landorus-I individually (in a vacuum) and in a team setting are both valid. You see, ladder players such as myself have gone out a tested Landorus-I, and some of us have found it suspect worthy (and yes, some haven't and I 100% respect their decision) due to our playtesting experience. This isn't theroymon, this is actual perceptions as a result of games being played. The examples being given are (often enough), actually, examples that occur / occured in games. This isn't the 1v1 metagame here, pokemon is played with 6 mons which is why there are certain arguments that address this. If real life playtesting wasn't relevant, heck we could prolly just have a vote right now.
So yes, Landorus-I is often mentioned with partners just like other past suspects (Tornadus-T with its Rain and (often) Dug + Tenta), Gene + Dug etc etc), and while its true that sometimes, users have mentioned 2 pokemon vs 1, largely this is due to lack of infomation (ie someone lacking a 2nd pokemon). You just cannot throw out a "well Specs Latios beats Landorus-I end of story" simply because if you try that in an actual game, chances are you risk losing your Landorus-I counter / check. I think that this is the point some people are trying to make.
Anyway
This post has already gone on for far 2 long, and in feeling unwell atm so ill cut it short. Basically when you are throwing around checks and counters, please don't assume that Landorus-I lacks team support. I'm not expecting a full 6 vs 6 importable with pages of text summarising what happened on Turns 1-15 of your scenario, but mentioning something that can be pursuit trapped (when Tar is Landorus-I's #1 partner) and then yelling NOP DON'T MENTION TAR COS ITS JUST LANDORUS (not saying anyone actually is) doesn't cut it anymore.
TY if you actually read this tl;dr