Diggs has been hurt since he signed his deal. I don't blame a player for tearing an ACL, and I don't expect them to be fully recovered in the first season back from that.
I don't think fans are "providing an open and honest evaluation." I think they have been mad at him since he missed a tackle against Kittle in the San Fran playoff game where he was trying to put a hit on the ball and Kittle made a move and made him miss. And ever since then, they get mad ever time he misses a tackle or for his effort, or lack thereof, on some tackles (even though he's also come up and made big hits at times).
Diggs signed his contract in July 2023 and tore his ACL that August. He didn't play all of last year, and this year he played coming off of that and has tried to play through more injuries. So how he has played since he signed his deal is not very much, and QBs still mostly avoided him when he played this year, choosing to throw against rookies and cheap free agents on the other side.
I hate that he hasn't been healthy and that he and Bland didn't really get a chance to play together this year, but that's bad fortune, not a bad player.