If you're any character except a Nord, the only logical choice is the Imperials.

This is so wrong.

Yes, a Nord would be most likely to join, but a Redguard would also very likely join the SC over the Empire during Skyrim. The Orcs(from Skyrim) would also have a reason to fight for the SC, the SC don't bother the Orcs, but I doubt the Dominion would just leave them alone. All of the other races could have personal reasons.

The Stormcloaks are xenophobes and Argonians are usually kept in the slums in the Stormcloak capital of Windhelm.

They actually can't even go in the city... although to be fair I don't think anywhere is exactly welcoming to Argonians, even in Cyrodiil.

Basically the Stormcloaks would use you for your power to help win the war then either exile you or (more likely) stab you in the back - assuming the story went that far

That's what the Empire did to Skyrim and Hammerfell! You are making something up to hate the Stormcloaks over, while the Empire did exactly that lmao.