While I agree that it's very frustrating for player who didn't abuse in any way, I believe the reset was necessary.
I think the problem is that it's much harder and slower to advance from the lower leagues in SoulKeep than it used to be in Splinterlands when there were level caps in the leagues. And while in Splinterlands there was no issue with having a max card vs. a bunch of lower level ones, in SK it's actually a disadvantage because the lower level ones have the same effect and each copy can be played the same number of times.
I believe SK is also more punishing to take away time from the game. In Splinterlands if you do you just don't earn glint and SPS. Maybe drop lower of you played a few games that season. If you didn't play, you stay where you were. In SK everyone else is advancing but you on your break.
Still think it was awful and they have now lost a player on my side. Going to rent all my cards out instead...
But I find it hard to rent out cards. I have the max level legendary heart card and the bids on it are very low.