I am struggling with coming up against 1700s as a 1500

Something I think is unfair about the rating system which is that now I have reached 1500, I face many players whose previous peak is 1700 or above. Of course they destroy me, which causes my rating to slip again. I have noticed there are a lot of ex-1700-1800 players who, for whatever reason, are always playing at the 1500 level. It seems unfair that at my peak I have to play against people who previously peaked 200 elo above me. I can guess with almost 100% accuracy depending how they play that if I click on their profile I will see a peak of 1700+

I doubt you are facing many sandbaggers. I would say this is very common. On some days, someone might drop by 100+ points because they are tilting and aren't playing their best, but when they come back, they'll be playing in their best form again.