The thing is, Garuba has the upside to be more than a rim runner. Sure, if he ends up as an undersized center, like a Jordan Bell, then his value would be low. However, he's shown he can play with grown men in probably the 2nd and third best basketball leagues in the world. If he develops enough offensively to hang as a 4, then his defense alone will be worth it, he can legit guard anyone 1-5. Now, I can understand if people don't buy his shot would ever develop, I can't say I understand enough to be able to judge whether a player can or cannot improve his shot.
He has shown improvements this season, though, he's practically shooting and hitting 3s at exactly Evan Mobley's rate. It's not great obviously, but this is why we're keyboard GMs and real scouts' jobs are difficult.