I think the problem is that on both sides of fandom, the concept of a “redemption arc” has gotten twisted to a point where it’s basically meaningless.
See, a lot of the time when the woobifiers say they want a “redemption arc” for their fave, they don’t mean that they want that character to have to face the awfulness of what they’ve done or put any actual effort into changing or face any real consequences. They basically mean that they want the good guys to realize to realize their fave wasn’t so bad all along and have them hug it all out or something, with maybe a token nod to the villain feeling regret, but nothing that really holds them accountable.
So of course if you’re thinking of “redemption” that way, you’re going to have people on the other side saying “This character doesn’t deserve redemption! They’ve done awful things!” Because yeah, they don’t deserve unconditional forgiveness and support from the heroes. They don’t deserve to have the slate magically wiped clean as if all the bad things they did never happened. But that was never supposed to be what a redemption arc was about. Real redemption is long and messy and hard, and it takes a really good writer to pull a proper redemption off. But when it is done right, it’s not about letting the villain off the hook - it’s exactly the opposite.