Kongbo supposedly has great speed and quickness. I've never seen it though. The thing about Phillips and Kongbo, and McKenzie too when he was here, isn't that they are terrible. It's that an opposing offense doesn't have to account for them in any special way. They aren't getting blown off the ball every play, but if an opposing offense puts a hat on their hat, boom, they are blocked and taken out of the play. Easy enough. None of those guys are play makers or difference-makers. I could understand it if they were all 3-star recruits, undersized, or lacked athleticism. But they don't. What makes defensive linemen special players are the fact that they have to be specially accounted for by an opposing offense, which makes it easier for other guys on your defense to make plays, and even though they might be specially accounted for they are still going to make plays.
I looked it up the other day and saw where Kongbo and Phillips, combined over each of their Tennessee careers, have 6.5 sacks. This is over 6+ seasons. That is a mind-bogglingly low number given how highly touted and recruited they were.