Overall it's a very solid team. The Gengar, Gyarados and Dragonite should be able to sweep through most of the Elite 4. Just make sure to bring plenty of potions and revives. The only thing I would mention is, try to get some of them to around level 85 as they'd likely be out-sped by a lot of the E4 Pokemon. Best of luck :Smile:
Thank you for the tips @JollyolNathan I wish u the best on lucks on ur journey