Landorus-I is a solid offensive threat with Sheer Force, but is mostly outclassed by the likes of Genesect and Greninja. Landorus-T is a really solid Def pivot, Thundy-I is a good offensive support. Thundy-T is decent in rain but rain isn't that great anymore. Don't know much about Tornadus.

A properly supported Choice Scarf Terrakion/Garchomp or bulky Landorus destroys your whole team, and you have nothing to check them. All of your Pokemon save Gogoat and Volcarona are weak to the ever-ubiquitous EQ and the infamous EdgeQuake combo takes care of Volc. All Genesect variants can also sweep your team after an SpA boost by spamming Flamethrower, Bug Buzz or TBolt which are all standard on Genesect. Also, you lack a strong scarfer or revenger, and your team is really slow overall so you'll need one. After Volcarona and Tentacruel are gone, you're walled to hell and back by Skarmory, and your whole team bar Volcarona is walled by Ferrothorn. Volcarona isn't that good anymore, use Charizard-Y if you need a strong special Fire sweeper. It's faster, stronger, and isn't OHKO'd by Talonflame. M-Mawile seems very underwhelming too FWIS, so you might want to throw in a revenger such as Talonflame who also helps alleviate your Ground weakness.