He shouldn't be untouchable BUT we're not seeing what he can really do because Duane Casey is not the coach who's gonna help him develop into the best player he can be. Assistants and such will help but ultimately the Head Coach could be the determining factor for talent like Valanciunas.
Casey isn't good with young players(as seen with Acy,JV and Ross),which is the number one reason why he should not be back next season if Ujiri and company wants to rebuild.
Ideally if JV could be like a Gasol that would be excellent,even if he turns out to be a Noah that's good. I'm rooting for him,they just need to continue to feed him until he becomes comfortable being a focal point on offense,he's already intense so his defense will get better naturally.