He's just too limited offensively... I'm not even talking like he needs a jump shot or post moves... I'm talking like when they switch Bev to him he needs to at least be able to seal him and hit a small baby hook like Zubac, Ayton, and other offensively limited centers can.
He can't pass, shoot, handle the ball... his screens are great but impact gets limited by teams that can switch... well all the best teams that have won titles are capable of that. So if you have Don and Mike you might be okay letting them go to work... but then you are really iso heavy and Rudy will just sit in the dunkers spot... can get some offensive rebounds and stuff but I'm not sure that wins you a title.
I've often wondered what the offense would look like with a big that can make passes in the middle of the floor... How much better could the offense get? It might not get better from an offensive rating perspective but you might get a few more quality paint shots to mix in with the threes... I know shooting 40% from three and 60% from 2 has the same point per shot value.... but the variance between those options is huge. Teams routinely go through droughts of 10+ missed threes and that variance can lose games for you... sprinkling in some of the other shots can help you weather those droughts a bit better.