That's a good point. IMO, here's how I might handle it. Stormtroopers have different stats, depending on what book you pull them from, like from the Thrawn Trilogy sourcebooks, or Rules of Engagement (I think), for varying levels of power (based on their skills, but also their gear, like troopers getting thermal detonators, etc).
I would give every stormtrooper variant access to the (Knowledge) Tactics skills, but as a specialization for the environment they specialize in (probably Survival in that environment, too). These guys? "Tactics: Tropics".
If the GM decided to put that skill to use, think of turning a tropical place into a warzone, with combat raging for a longer period of time than Rebels anticipated. Hours, a day, a week, maybe several weeks. The rebels come with whatever they can bring, maybe geared for sunny weather, but not rain, or floods, or extreme winds. Tropics can flip-flop back and forth at any time.
Stormtroopers trained for this, with the right gear to handle such a thing, would easily triumph over Rebels who are more than likely ill-prepared for such environmental combat. Even better, their training and tactics might involve forcing such a battle to be stretched out on purpose, to make use of these specific environmental changes or hazards.
Now, imagine what happens if you throw in some weather control tech under Imperial control with THESE guys, and what happens????
I'd take the same approach woith aqua troopers, desert troopers, zer-g space troopers, etc.