Actually there are only Embiid and WCS, Vonleh is just a consolation prize, strictly a PF who competes on D and has enough athleticism to be an impact defender in time.
I've seen Indiana play a few times this year with the express purpose of watching Vonleh. I still have 5 games recorded that I need to watch to catch up on the season. Right now from what I've seen I would agree with you to some extent. Embiid and WCS definitely look to be the better shot blockers, but they also appear to be able to also play the Center position which means that they are just longer than Vonleh.
Vonleh does look to me to be really a PF with-out much of an ability to effectively defend the bigger centers in the NBA, but from what I've seen he definitely has athleticism as well as defensive awareness, so I think there is a good chance that he could develop into the defensive PF we want next to Cousins. Granted I've got 5 more games to watch, but that is just my initial impressions.
Do you remember Tristan Thompson from Texas?
I remember watching Texas play to watch him and Jordan Hamilton and Cory Joseph play. I started the season focusing on all three, but stopped really watching Tristan because I didn't think that he had the potential to be much better than JT. The Cavs shocked me when they took him #4 as I thought it was an utter reach.
Well, so far in watching Vonleh play I haven't gotten the same vibe. I think that he would be able to come in and force JT to the bench, and any sort of PF that we can draft that can do that represents a 'win' in my book.
So though I might currently have Vonleh as the 3rd of the 3 defensive bigs, that by no means makes me think he can't come in and play the role that we'd want of him.