Two things:
Those four players mentioned... ALL of them were good acquisitions. No, Khris for Kuz was a bad player trade off, but the trade did much more for getting the Bucks under the second apron so they had the ability to make other moves. Herro and Turner are valuable assets...just not in the Buck's team-rebuild window. LeVert looks like a useful player that we got in a salary dump for table scraps. So if these are your examples of how Horst is a bad GM, you have bad examples.
Trying to bring in talent and make trades with Giannis on the team is much harder than people remember. Not only does he consume a huge part of the cap with his salary, he did as much damage with trying to keep him happy (signing his brothers, getting the bad coach he wanted...twice, constantly trying to stretch his playoff window...). I think there is a reason why LeBron keeps changing teams... the superstars suck the resources of a team dry and then when they can't build around them anymore, they move on.
Interesting to note that LeBron only won two championships while with the heat. And that took him leaving in FA, forming a super trio and won in back-to-back years. Something that could've easily happened with the Bucks (or even 3 years) if it wasn't for health reasons with Giannis-Mids-Holiday trio. Of course Lebron left for Cleveland for a single championship and then had to leave for LA for a single championship.
I think we are going to find out that Horst is a better GM than we give him credit for...