Donovan can't be both a poor defender and an inconsistent playmaker. He is great at shotmaking because team works for him on offense and he doesn't have to be burdened with playmaking duties. He is no Luka or Trae, he isn't able to read the game naturally.So who is a good fit next to an undersized 2-guard who plays no defense and likes to play hero-ball? IT's very hard to get a 6'5 defensive PG who can also shoot and playmake for others (to make up for Don's inconsistent playmaking). Other than being short Mike Conley is the absolutely perfect guard next to Mitchell. He's about a good of a fit as it gets.
The answer is Donovan should just become a better defensive player. He doesnt even have to become a good defensive player, just be average, which he should be able to do.