I presume resetting the ladder ratings is off the table? Given that it was messed up for so long by a calculation error of the teams elos, it doesn’t seem like the wrong thing to do, although I’m sure it’d probably annoy too many people.
If the devs had a match history list for every player in principle you’d think you could try and recalculate/readjust the ratings of players, although even in that case it could take far too long.
Maybe some kind of rescaling? Squash all the ranks toward the middle/average but try to keep the ordering?