I'm truly convinced that Dubois is no worse than them and that on a good day he can defeat them all, he's naturally bigger and stronger than them...
Quarry is considerably smaller and the size difference might be a bit too much. But Quarry did well vs big punchers he schooled Ron Lyle who was a pretty big guy and a big puncher. And Dubois was floored multiple times by a former Cruiserweight. I'm not sure if the size difference would a bit too much though.... Ibeabuchi and Witherspoon at their best both beat Dubois.
Quarry has the skill but i don't think he can keep Dubois off him. I know he did vs Lyle but i still think Dubois has a better harder jab than Lyle. I think Dubois's jab will allow him to set up his power hand and stop Quarry after a competitive fight. Dubois tko 9. Ibeabuchi is a bit too durable and should be able to stop Dubois. Ibeabuchi tko 8. Witherspoon vs remarkably inconsistent. I think it will be very competitive. Witherspoon has the better defensive skill so Witherspoon by competitive decision.
In my opinion Ibeabuchi would have smashed Dubois. With Witherspoon I think Dubois would have been favored (I'm talking about the Dubois seen against Joshua, not the one who faced Lerena), while with Quarry it would have been a good match, probably close, and perhaps Quarry's tendency to cut himself could have been decisive (see Hrgovic).