Why would you think? Sanderson draft 5oa in a much stronger draft class.
Sanderson is a little bit of a mess in so far as his development years were impacted by the pandemic and injuries. But we shouldn't be mistaking his potential which is to grow into a top pair D. And based on track records of other high end college picks that stayed the extra year in college, projecting that he's playing at a top pair level by mid 23-24 isn't out of whack.
Dobson is a great player. I think it would take Sanderson+ to get him. Not because he has a higher ceiling though. Because he's in the league and playing at that level. Sanderson isn't.
Patience