I agree with the other assessments, so I'll suggest replacements:
1. Lugia: should be stall-oriented
2. Volcarona -> Reshiram
3. Genesect: Nature = Mild or Hasty - losing defense is not as important in Ubers since most of the attackers are specially oriented so you only have to worry about Mewtwo X or Arceus, things you'll probably just U-Turn out of. Also: Bug Buzz and Extreme Speed -> Thunder and Ice Beam. Bug Buzz has poor coverage in ubers, only super-effective on Mewtwo, Mewtwo-Y and Darkrai. Extreme Speed is weak. Thunder will be the perfect revenge kill against Kyogre since you'll be faster, to weaken its Water Spout; and is also super-effective on Ho-Oh and opposing Lugia. Ice Beam for coverage against Rayquaza, Giratina and Groudon. Despite the poor coverage, you should keep Flash Cannon because Xerneas is everywhere.
4. Gardevoir -> Xerneas
5. Gengar -> Deoxys-A
6. Forretress -> Dialga, Deoxys-S (note: I'm assuming you just want to set hazards and not rapid spin, Dialga is the best in Ubers for simply Stealth Rock, with Deo-S if you want both Rocks and Spikes, tho you can't have Deo-A and Deo-S on the same team.)