Haunter, why you still gotta hate on Abomasnow? :( I already noted how it can be a perfectly valuable pokémon and simply building your team with the knowledge you're using Hail. Whether or not you specifically use pokémon that take advantage of it, like Blizzard users and more Ice pokémon, puts you at an advantage over the opponent.
Scarf Cresselia for Garchomp counter, woo !! It's a lot less of a gimmick than it was Pre-Plat too. Now it learns Trick. :P I'm just being facetious here but it does work. What's the calc for Hippowdon? And don't forget that Gliscor also has Sand Veil, so you might miss it!
Even SD Garchomp needs to use Outrage to OHKO Swampert dude, Earthquake only deals ~90% to even 252/0 neutral Swampert. Forcing it to Outrage isn't all that hard either, since SD sets pretty much have to use it against any Ground resist/immune that isn't weak to Fire. (And if it's Sub/SD, it doesn't even have a Fire move!)
Whoever said Latias can be easily countered... no. :[ Just no. And I'm glad some other people are finally realizing Kingdra's sheer power without me having to restate it myself. Vaporeon is somewhat effective against Kingdra not because of Water Absorb, though, but because it very commonly carries Protect and can stall out the weather easier than most other pokémon. It can do absolutely nothing to kill it, though.
If Garchomp does nothing to your team even with SS active, then either you face really bad opponents, or you're an extremely lucky player.
Why is that? We've basically already established that, even with bare minimum "Garchomp checkability," it only has a 1/4 chance of outright sweeping with
one particular moveset and with Sand Stream running. Garchomp isn't being super-effective (*rimshot*) 3/4 of the time even with that moveset. It's probably even less dangerous with any other moveset and its effectiveness is dramatically decreased against any team with Skarmory or Bronzong. (Skarmory in particular due to the Spikes it lays, in addition to walling all non-SD/three attack Garchomp sets.) I have no problem imagining plenty of teams not having much trouble with it.
Besides, Sand Stream is Garchomp's major enabler anyway. I'm not going into that one again...
I won't repeat my opinion on revenge killing. My point is that there are no safe switch ins into Garchomp, and that to "safely" beat it you often need to sacrifice a potential counter... it can't "easily be countered" as you stated before.
Indeed, you are correct about revenge killing, though it still helps in comparisons. For example, Salamence is tougher to revenge kill than Garchomp because it can boost its Speed, thereby rendering most Speed-based revenge killers (e.g. Scarf T-Tar, Starmie, Infernape) ineffective and requiring either really fast Scarf users or priority to revenge. Just saying "you can revenge kill it!" is obviously not a useful statement to make.
But, you know, there's no safe switch in to Salamence either. :/ Your primary argument against it is that it can just be "worn down" through residual damage. All that does is more it easier to revenge kill with Scizor/Dragonite/Lucario! (Ice Shard users tend to kill both Salamence and Garchomp, while Salamence is better against Fighting priority.) You still have to sacrifice something to "safely" beat it because there is no universally safe switch-in.
HP electric on a bulky water is basically only for Gyarados, but its pretty easy to do. You cant just chuck HP ice on on Celebi and not worry about Garchomp any more (trust me, I have been using it).
Sure you can, and sticking a random Ice move on a pokémon is generally more useful than a random Electric move too. Maybe not HP Ice on Celebi in particular but you could put Ice Beam on T-Tar, which also hits all the other bulky Ground pokémon that tend to cause it trouble, except Swampert. HP Ice on Jolteon also hits Grass pokémon which resist its STAB. HP Ice on Rotom... okay not so much, though it could also tank a hit from Salamence in a pinch and KO it. Ice Punch on Jirachi and Metagross, blagh blagh blagh.
getting rid of Ttar isn't easy, and if you do use rain dance a good player will just remove the rain dancer then bring Ttar back in again.
Getting rid of T-Tar is easier than most other pokémon. It resists none of the entry hazard moves. It's easily lured, due to its propensity for Pursuit trapping enemies (or at least switchin in and pretending it will). Dugtrio destroys it if T-Tar is that much of a problem.
Rain Dance in particular scares T-Tar (and Hippowdon) because it's heavily based on Water pokémon, which T-Tar will have a hard time even switching in against without eating a super-effective attack. They also have multiple Rain Dance users, since their "ez-street" route to weather is Uber. :/