Previous season MMR should only carry on during placements
It is insane how people can have a negative win ratio and be in high elo (diamond 1/master/grandmaster/challenger) just because they were diamond 1 or above last season.
This just ruins ranked honestly and makes people who actually lost it get to a rating they barely had to work for.
Back in season 1-2, rating was high value, because there wasn't much in the game and previous season MMR didn't get brought season to season 8 times. This was an issue that was brought up a few times in the distant pass but no one really cared.
So yeah, due to how many seasons there have been, I think it's time to only make the game take your MMR into consideration during placements and then treat the account like a new account, not taking into consideration your previous season standings.