Sorry for the late rate, exams and shit.
Well this is a pretty nice team for what is essentially a gimmick. You're the first dude I've seen in awhile actually who's team isn't set up bait for Lucario or something lol. Ok lets discuss offensive synergy first. As long as the sun is up, your offensive synergy is pretty good. I don't like Donphan really (although it is needed to avoid being 6-0ed by a Salamence) as it can be set up bait, but as it has the important role of setting up Sunny Day, I don't mind it as much here. My main gripe # 1 is that you have alot of set up pokemon, but you have what, two pokemon that can properly take advantage of it (Heatran can't really as it is a revenge killer limited by Choice Scarf). Rotom should probably go, you don't want to lose one of your sun users to crap such as Pursuit now do you? However, you don't want to be beaten by Empoleon either. Zapdos does a similar thing, except is very Stone Edge vulnerable, which isn't exactly good either. You could actually run Sunny Day Bulky Flygon if you wish, it helps prevent Empoleon setting up (aside from Azelf, it doesn't really set up anywhere too easily) and it isn't weak to Tyranitar either. Earthquake/Roost/Sunny Day/Dragon Claw possibly? I dunno, Rotom seems better suited for the role, but the most important thing for weather inducers is to not be Tyranitar weak, due to SandStream. As for a defensive perspective I've noticed that you are really really weak to Calm Mind Latias. I'm actually struggling to find a counter for you that either doesn't have SandStream or isn't enormously Fire weak. Steels and Tyranitar are really all that stops it, and whilst they are usually commonplace enough on most teams to make Latias more of a non-issue, on yours they both are counterproductive. Maybe find something to plug this hole?
Ahh sorry my rate was pretty shit for my standards, I have trouble with rating gimmick teams like this because I haven't really played a sun team myself, so I don't really know the intricacies required to give you the rate you deserved.
Hope my little bit at least got you thinking about your team, if nothing else.