That is correct as long as you don't hit the corner cases.
73 karma · joined June 13, 2017
Reviewing a paper is mostly charity and gets you nothing in return, except the fact that when you submit a paper, someone will do the same. It does not help in the Green Card process at all, or boosts your academic credentials.
Regarding overworked professors, they are allowed to delegate reviews internally to students to ease the time they have to spend.