Nice write-up here, you're right that S83's will be guinea pigs of sorts. They will be the first class to fully experience the new depreciation system as a 9 season player in the S83 class will face all 4 depreciation hits. It'll certainly be interesting to see how they manage, and I hope we gave them all enough time to adequately adjust as well.
Regarding the pre-hybrid stats, we're getting to a point where very few players will exist in that range. It's really just the S80 and 81 players that experienced the meta era, but they would have been rookies and sophomores so generally not a ton of points. For some assurance, we do factor in the eras and scoring trends when discussing players for the HOF, so don't worry about the S80 stats vs S83 players' stats at that point.