A prime VItali is so much wrong for Joshua. If it's Wlad's Joshua against Charr's Vitali, I might take Joshua, honestly. If it were a fun betting opportunity or something.
I'm not sure Vitali stops AJ but I am sure he administers an old fashioned beating. This is a horrible fight for AJ and Vitali simply beats him up from bell to bell.
His chin being of the level that he avoids being one-shotted or not, he is obviously not that durable at top level and cannot recover well so is vulnerable to being stopped. You can argue the toss as to whether that's down to chin or heart - I actually think he was basically concussed against Ruiz and DuBois and that this speaks to his underlying chin issues. It is really just semantics - the effect is the same. If they can get him out of there, it's very possible Vitali can.