Snoke I think was respected as a character mainly because he had so much mystery and potential as a villain in the Star Wars Universe, not because of what he actually did in the movies. His death scene in TLJ is arguably the most asinine plot choice made in that movie (Which is an impressive feat) due to how many questions were left unanswered. What was his overall goal, where is he from, how did he get to the position he is in, his true feelings of Kylo as an apprentice, Rey as a possible candidate for the dark side, etc.
Rey is the most blatant example of a Mary-Sue character I've ever seen and I dont find her interesting at all (poor writing, not poor acting). I cannot see why people would genuinely think she is a well-written character, but I can fully understand why people cut Snoke some more slack since he had potential whereas Rey arguably does not.