I agree that perimeter defense is the problem, but I think it's perfectly fine to place at least as much blame on Griffin for not being willing or able to adapt to the personnel. It's a bit crazy, but the Bucks' defensive rating with Lillard on-court is actually better than their rating with Giannis and Lopez on-court and Lillard off, which shows that Lillard might not be the absolute centerpiece of the issues.
(Last season, the Giannis/Lopez on and Holiday off defensive rating was 110. Right now, the Giannis/Lopez on and Lillard off defensive rating is 125.)
I'd agree that they shouldn't have fired Budenholzer for Griffin, though I was okay with them firing Budenholzer at first because I thought the obvious choice was Nick Nurse. For the Lillard trade, I don't think it was bad in a vacuum--it was a calculated risk that having another go-to guy to rely on offensively in the playoffs would outweigh the defensive downgrade. However, their inability to adapt and inability to replace role players really escalated the challenges they were already going to have.