Then stop complaining about Dragonite being more useful in RAIN, when Sun plays a part in this team aswell. Tropius is here to benefit the sun side of the team, which he's a monster on. This team is made to be sun/rain to make the most of abilities that can be utilized during these weathers, to, and if that Tropius is being used in the effects of sun, it'll be monstrous (provided it has solarbeam).
Also, you're highly exaggerating. No purpose on this team? I don't think you get the reason why this Venusaur is physical. It's because Tropius is a deadly threat in it's own right (provided that you replace Silver Wind, Explosms).
Oh... I think there was a certain reason why Dragonite isn't seen often lately... what was it again? Oh. Mhm.
My point is that Tropius is just as viable on this team as Dragonite could be (oh, and if you're facing another rain team your dragonite will have a lot of fun trying to take Ice Beams while trying to use Hurricane, which has subpar accuracy). Whether Explosms chooses to keep any two of Heatran, Tropius and Dragonite is up to him. This is an RMT, where you're supposed to recommend decisions and explain the reasoning behind them, not just slapping some random set on and arguing about how a certain pokemon is shit without giving some more detail.