I have played ADV for about a month, so my opinion really doesn't hold any weight. But from my experience, the top 10 threats are:
1. Tyranitar: Single handedly makes Endure+Reversal not viable, most versatile Poke in the tier, fantastic movepool, great all round stats, and can fulfill any role you want it to whether it be sweeper, tank, lure, stallbreaker.
2. Jirachi: Okay, so SubCM Jirachi is a god even in ADV, Superachi and CM Wish are both fantastic sets as well. It has great typing, great bulk, and the most annoying ability on Earth.
3. Salamence: Even though this thing has to rely on Hidden Power Flying for damage, it still shits on like half the Pokes in the tier. It is without a doubt the #1 sweeper.
4. Metagross: This. Thing. Is. A. Beast. It tanks physical hits like a boss and can absolutely pummel with its incredible physical attack. Very few things can take hits from this thing, and when its done its job, it can go boom.
5. Suicune: Taking out Suicune is like beating the hardest boss in a game, the thing just has so much natural bulk that you cannot take it down in one shot without Explosion. It can just CM, Rest when needed, and tear shit apart.
6. Gengar: Dangerous for the simple reason that it catches Explosion. So many people rely on Explosion to take out the likes of Suicune and Snorlax its not even funny. It also is one of the most versatile Pokemon in the Tier and you never know what set its running until its too late.
7. Flygon: This thing is just plain so underrated. It resists Quakeslide and can use Quakeslide coverage itself to hit hard. Flygon's excellent typing makes it easy to come in and out, making it an ideal hit and run pokemon.
8. Aerodactyl: There is nothing more rage inducing than CB Rock Slide flinches from Aerodactyl. As long as there's an Aerodactly still in the wings, the match is never over.
9. Celebi: Leech Seed+CM+Recover+STAB is one of the most annoying sets to deal with. You really can't beat it with status since it can just switch out. You really can't set up on it since you get Leech Seeded. The single reason so much shit run Hidden Power Bug.
10. Snorlax: Sure this guy is not the same one man army as GSC Snorlax. But it absolutely cannot be underestimated. Most people's responses to this thing is phaze and deal with later, because there really is no safe way to deal with it. You mentioned Tyranitar+Gengar+Metagross trio shuts Snorlax down completely. Well, thats just more argument that Snorlax is beast, I mean, you need THREE elite Pokemon to keep it under control.