You do realize that even if Sunny Day is in effect, it can't hurt anything with its mediocre attacking stats unless we bump it up in an evolution. With a 4x weakness ot Ice, 2x weakness to Poison, Flying, Bug, and Dragon, it doesn't make a good tank/wall considering that all good teams run at least 1 of those attacks. All the other Dragons have at the most 3 weaknesses, Rock, Dragon, and Ice for Mence/Altaria/Dragonite, so this new Tropius Grass/Dragon Evo is going to be outclassed in almost every way unless we gave it insanely ridiculous stat distributions or a signiture move or trait that makes it stand out.
You do realize it will be the first and only Dragon that can utilize Subseed, and 2 STAB 140 BP moves.
Tropius also has Swords Dance. Really, Tropius's problem is that its stat distribution isn't that great, it has an awesome movepool. It's worst problems specifically are Skarmory and Bronzong, and they are already thorns in the side for loads of pokemon.
Consider also that we'll pretty much be forced to keep abilities. Lets say this is on a Sunny Day team. Solar Power would give it an insane SA to use Draco Meteor and Leaf Storm with. Given the same EV's and nature, that beats Specsmence by a small amount. And that's with its current stats. If we bump it up from 72 to say, 92, it will beat Specsmence by a mile.
Further still, depending on how useful areas become, Tropius has Nature Power and could theoretically do anything from Hydro Pump to Shadow Ball.
I mean really:
() for Dragon moves sure to be added.
Support:
Whirlwind
Roar
Leech Seed
Roost
Synthesis
Sunny Day
Swords Dance
Growth
Curse
Physical:
Leaf Blade
Aerial Ace
Earthquake
Body Slam
Steel Wing
Rock Smash
(Dragon Claw)
Special:
Air Slash
Energy Ball
Grass Knot
Leaf Storm
Silver Wind
Hidden Power
(Dragon Pulse)
(Draco Meteor)
I mean, for a Grass type this isn't that bad at all.