I think the need is to upgrade as many rotational pieces as possible to players who are at least passable on both sides of the ball. The biggest issue I saw throughout the season, including the GS series, was the constant conceding of one side of the ball for the other, especially on the perimeter. HB, Keegan, Huerter, Monk, and TD all were massive defensive liabilities for one reason or another. But throw in Davion to improve your defense and you essentially have an absolute zero on the floor offensively, especially in our system where his primary role offensively is to be a floor spacer, which he can't do consistently.
Game 7 was exhibit A: put in TD because he can make the few threes that he did but concede what was matador like defense to Curry that resulted in his 50 point outburst. I know, I know, Curry is Curry and he certainly could've done the same to Davion--there were plenty of times throughout the series where Davion's perfect defending of a play still resulted in the Warriors making an extremely difficult shot--but he would've at least provided some sort of resistance and made everything tougher (especially getting into the paint, which Curry did at will).
This upgrade could certainly be internal. I hope we see Keegan grow defensively, for example, but he struggled all season to stay in front of opposing players' first steps and was hunted defensively for it consistently as a result. It could be Monk and Huerter improving their defensive awareness and not losing their man as much off (or sometimes even on) ball. Ultimately, I think the path will be upgrading Barnes' starting spot with a better 3 and D Kessler Edwards type player. This is why we talk about how incredible guys like OG or Mikal Bridges would make this team, but they're obviously not attainable. Maybe Kessler or Keon Ellis can even develop into that guy. If I'm them, I'm spending all summer becoming a catch and shoot 3 point sniper, and I think combined with the defense that could earn them a consistent rotational spot if not the starting spot in place of HB. Clearly i don't think retaining HB is the answer. His spot just seems like the most logical place to upgrade given his contract situation, age, and style of play (Keegan and Huerter's shooting being pivotal to our offense).
Find that Barnes replacement and a big with size who can protect the rim and isn't completely useless on the perimeter like Len (i like this Garuba talk or again maybe internally with Queta if he's ready and able) and I think this team takes a huge step forward.