depends on the situation... most pokemon don't have pokemon you can just switch in on. that is why they are OU. Scizor can switch into HP ice for instance. Gengar can switch in to EP and FB. Any flying or levitating pokemon can switch into EP. All rotom formes can come in basically for free.... It just depends. If I were to say anything you would come back with a scenario where you just made an amazing move or you have such and such counter. Landorus has plenty of switch ins. unless your opponent has u-turn which is a plus for me because now he loses 10% and another 12% on the switch in so he probably won't do that again.
Okay, but those aren't necessarily better switch-ins. Assuming the standard Earth Power / Focus Blast / HP Ice setup, SpDef Celebi, CM Latias, and SpDef Jellicent switch into all three pretty easily. None of the Pokemon you mentioned can switch into all three like they can besides maybe Gengar, which is hardly a defensive Pokemon (I'll give you that one, though). And yes, I know that not all Pokemon have reliable switch-ins, but again, this was all about "key" defensive Pokemon and whether they can KO Landorus or not. Not everything you mentioned can do that.
In addition, Landorus may lose 22.5% health from that ordeal, but your counter might have also switched in on Stealth Rock and taken a bit of damage from U-turn, and now your opponent has the momentum and might force a bit more damage from Stealth Rock and whatever attack they use. Landorus might take some damage, but you hardly came out on top.
I just bring it in on the revenge...Having one of your pokemon just get killed is one of the most useful momentum gainers in the game. since HP ice choice scarf is so shit you would never expect it... Dead landorus-i...He gone
Oh certainly, but there are still problems with that as well. For one thing, you're talking about a revenge killer. That would require you to let something die every time you want to bring Celebi in, and if you're doing that, you're going to get behind really fast. Now, that wouldn't be a problem if you're actually able to kill off Landorus, but in that case you're just hoping that the Landorus user goes for the U-turn and doesn't just switch out. In fact, if it doesn't have U-turn at all, it most likely will switch out. Now your opponent just switched something into your weak HP Ice and you're behind again.
What I get is that Scarf Celebi is a mediocre set that you're using mainly to keep Landorus in check. It's a neat set and all, but it really doesn't have many other advantages over other Scarf users. You do well against Sheer Force Landorus (provided they actually stay in to take the hit), but the other 94% of the time, you're using an otherwise inferior set.
Because the biggest arguement is that landorus has tyranitar to systematically remove it's counters... (although celebi doesnt work anymore because of baton pass). Do you think tornadus would have been uber without rain? Fuck no. It would have been in FU tier without rain.
The only reason that the deal with Tyranitar is such a big argument is because there is a debate as to whether or not Landorus should be banned on account of Tyranitar's support. There are many other qualities that add to Landorus's possible brokenness such as it's raw power, coverage...pretty much everything I mentioned before, but those are less debatable. Tyranitar's contribution to Landorus's brokenness is a subject of much more debate, and so it is discussed more, but that does not mean that it's the only reason Landorus is being suspected right now.
As a side note, of course Tornadus-T wouldn't have been banned without Politoed, but they certainly aren't the same thing. Tornadus-T's main STAB goes from perfectly accurate to very unreliable when Rain is taken away, which makes it much less effective. Landorus appreciates Tyranitar's ability to remove a few of its counters, but it's still a powerful Pokemon with or without Tyranitar. Besides, some one could just as easily take your argument and use it as an argument for banning Landorus since, just as Politoed helped break Tornadus-T, Tyranitar might help break Landorus.