All to Wicked CJ:
Garchomp: There's a lot of big threats that outspeed Chomp, so they can't just sub until they get a free turn. Even then, they have a 20% chance. Assuming Leftovers, that means they get 5 turns. That's a 2/3 chance of missing over 5 turns. ono, they might kill one Pokemon by spamming Sub. So you bring in something else that's faster/Scarfed.
Not arguing that it's completely unquestionable, just that 'luck-based' isn't a problem if it doesn't make it broken, and being able to Sub repeatedly until the opponent misses isn't enough on its own unless it can reliably kill off multiple threats.
Excadrill... I did have trouble with Excadrill originally, I'll admit. That said, there are a hell of a lot of priority users around, and it only takes any two of them to kill Exca, generally. (Not to mention that not every team runs TTar/Hippo, so it's not really "if people aren't using rain or sun, they are most likely using Excadrill.")
Drizzle is the one that I absolutely cannot agree with in your summary. Yes, it might be broken, honestly. I've not had enough experience with it to say. However, the fact that it is 'pretty much autopilot' or 'takes no skill' has absolutely no impact on whether or not it should be banned. Tornadus has the same issue Chomp has in that it is relatively easy to revenge-kill with pretty much any Scarfer, and if Tornadus is broken in rain then argue that Tornadus is broken, not Drizzle. Nothing else on the team is broken - idly, I've faced more DNite in rain than Tornadus, but I think that's better at it, if anything.
Latios: No safe switch ins! Except for Ferrothorn. Or Scizor. Or Tyranitar. Or possibly even Blissey or Jellicent. And they're only some of the most common Pokes in the meta, it's not like they're specific counters or anything.
Having to have a counter to the biggest threats is a standard for any game. That is like arguing that Whimsicott is broken because it forces you to run some offensive Pokemon or otherwise lose - stall/phaze teams hate Whimsicott, but then it just means they need an answer to Whimsicott.
Just because something doesn't have a specific switch-in/counter, it doesn't make it broken. (Hi Wobbuffet!)