Your team gets pretty much annihilated by standard Sun teams with Venusaur and Dugtrio at its current state. Heatran is the only thing on your team that's able to beat Venusaur on 1v1, as everything else gets curbstomped. However, it is prone to get trapped by Dugtrio, a common pick for Sun teams, effectively removing your only check to it. Genesect can also take advantage of Dugtrio removing Heatran and proceed to completely destroy the rest of your team as nothing really stops it well. To avoid getting stomped by Dugtrio teams every time I'd recommend using Shed Shell on Heatran, which allows it to escape from Dugtrio's Arena Trap. While you lose the precious recovery from Leftovers, you won't lose your only check to a number of threats that instantly sweep you which is a nice advantage imo.
Another thing that could seriously hurt your team is Tornadus-T. It's very easy for Tornadus-T to beat your only Flying resist, Heatran, as it's weak to Superpower/Focus Blast, Tornadus-T's most common coverage moves. It will then be able to KO the rest of your team with Hurricane rather easily a bit later in the game where everything has been hurt by entry hazards. While you have a weather inducer of your own to reduce Hurricane's accuracy, you REALLY DON'T wanna switch it into a full power Hurricane as it means you instantly lose the weather war if it connects. In my opinion you could be using Bronzong instead of Amoonguss. Bronzong does a number of things for your team that will be quite useful. Number one, it gives you a nice switch in for Tornadus-T which your team lacks. Number two, it gives you an additional Dragon type resist. This will be very important as Heatran is currently your only Dragon resist, and without recovery it will have a hard time keeping up with CB Outrages etc. Lastly, it allows you to run Whirlwind on Hippowdon instead of Stealth Rock as Bronzong has nothing better to run anyway. I think that will greatly improve your team.
Last thing, use a Naive nature on Landorus. Naughty isn't really good as Landorus needs all the Speed it can get. Its base Speed stat allows it to outrun stuff like max Speed Salamence and Genesect, as well as Volcarona, making its ability to revenge kill more effective.
Here's the set you should use:
EVs: 252 HP / 4 Def / 252 SpD
~Hidden Power Ice