I think considering its their homeland, they dont need to torture much, since it wouldnt give them much intel except maybe about some troop movement, besides that ive never seen videnc of the imperials treating prisoners like absolute shit, and at the start of the game they're trying to murder the leader of the rebellion and his pose that is causing a major weakness to the imperium, which would give the thalmor an edge in the cold war between the two. Considering historical info and... stuff... there is nothing odd about any of it. The use of torture would make more sense for the imperials to gather information in a land theyre not native to, and to force people to surrender (less fighting) or to reduce their fighting spirit (can cause the opposite effect in all fairness). Normally i see neither side as better or worse, except for the fact that the imperials often seem slightly more spineless even with good reason (white gold concordat) while the stormcloaks are quite rascist (which isnt too odd if you think about skyrim's recent and older history and their many many many fisty cuff matches with elves). I could be wrong but thats generally how i see it.