Okay I don't think that Turner should be a DPOY candidate (he has weaknesses that can be really exploited in the playoffs), but the reason why him and Capela are considered to be borderline stars are due to their qualitative advantages on defence compared to guys like Drummond/Adams/Robert: besides their great physical tools that allow them to block and disrupt shots at high volume in the paint (shots at the rim are the highest value shot you can get), their defensive awareness make them low error defenders as they don't miss a lot of rotations and are usually in sound defensive position to contest shots or deter opposing players from attacking high value areas or making high value plays. Drummond/Adams are lacking in both aspects while Robert is lacking in the mental part of the game on defence, it's why he's posting very good numbers in per possession defensive metrics in limited minutes where we scheme around his defensive weaknesses.
Robert's passing and ability to be a massive lob threat will separate him from the big men mentioned above: he has the potential to be a decent positive on offence ala Draymond/Bam rather than being stuck as a neutral offensive player because even though both him and the other guys can't create their own offence, Robert can add value to good offences by being a high post passing hub and a huge target in the PnR where he can dive into the paint and either finish or make the extra pass with his aforementioned passing skill to maintain or even enhance the advantage created by his teammates.
Robert's issue is that he doesn't have great awareness and BBIQ: teams can scheme to take advantage of stuff like his defensive lapses and tendency to be casual with some of his passes to chip away at his impact, but if he ever puts it together we'll have an incredible player on our hands - he can be anything from Bam last year to a Gobert-like entity with excellent passing and some floor spacing.