I fully agree with this comment: https://www.chess.com/forum/view/for-beginners/why-are-low-rated-players-so-good#comment-111655068
I used to be around 1500 rapid with another account perhaps 2 years ago with 75% winrate. I haven't stopped playing since but switched to Lichess. I just renabled an older account on chess.com and I'm sitting at 1230 elo and having just a little over 50% winrate. On lichess I'm 1800 bullet and 1600 blitz. It definitely feels like the ~1200 range is much stronger than it should/used to be. Doesn't mean much, but I'm also 2800 in puzzles and beat all master bots.
There should be a system to regulate sand bagging and a person should be flagged if he loses more then say 15 games in a row, anyone that denys sandbagging just has something to hide because it is so obvious and it is getting worse quite fast