It's common because there are highly ranked out of HS lackluster sized combo guards in every draft class
I mean, he's playing better than many of the guys ranked ahead of him (everyone is ranked ahead of him). And just because they are combo guards does not mean they play the same. I don't know what's so lackluster about Amari Bailey compared to other guys on the board. His defense, athleticism, and passing stand out as NBA ready skills.
Common isn't bad either. Black and Bailey both have similar archetypes. I like Anthony Black and I think he's a top 10 prospect. I don't think Amari Bailey is a top 10 pick but certainly a guy in the mix for a late first round pick given his play.