I get the criticisms about the show but at his core I don't think they screwed Boba up. I think they fleshed him out to where he is no longer a mindless, voiceless, antagonistic bounty hunter, demonstrating that he has humanity but also can be vindictive still against those who vow to hurt him or those he cares for
I also think the entirety of BOBF was really meant to establish Boba's character even further--the story within BOBF, in my view, had Boba go through his arc to be the final and best version of himself.
To simply have Boba go through such development and then ditch the character afterwards, in my opinion, would be an actual disservice to the character.
What Tem's attitude towards the characters feels to me, is like that he wants to portray the mysterious Boba Fett we got in the OT still, but with the way they've taken the character that is no longer possible--in my personal opinion, to the benefit of the character and the larger story, nonetheless.
He had that epic train scene with the tuskens, he gunned down the crew that murdered his tribe, he attempted and put up a valiant effort to fight a god damn wookie , he rode a rancor, and he had an epic final stand against Cad Bane (which is something within the story I think should've been built up to differently, but as an event that happened it represents the edge he still holds, and how his growth beyond the stereotypical "bounty-hunter" figure-mold allowed him to best Bane, his acceptance of what happened to him and the abilities he learned along the way with the Gaffey Stick). This isn't mentioning the stuff he did in Mandalorian s2
If I were to be honest--this also may be my own ignorance on the subject, I must acknowledge--I've yet to see a genuine take on how they "ruined" him that I could see from how the narrative was presented.
I don't see him doing a quirky scene saying "ride it like a bantha" to be ruining him. If the entire show was him doing quirky scenes like that then I could see that point. But it's that same episode he makes that joke that he leads a full on assault on the train, has that incredibly moving initiation scene with the tribe, and even before that kills that sand monster that was going to kill him and the young tusken.