That was the problem as far as Dubois was concerned, where was the plan? He tried holding the centre of the ring with an aim to dominate via left hand jabs and then throw heavy punches with the right but it did not work because Usyk was happy to go around him and take the fight to Dubois whenever he wanted. It seems as though Dubois really did not have a plan (or if he did, Usyk never allowed him to implement it).
It is impossible to take anything away from Usyk, he deserved the win. For the fight end with a knockout in the fifth round against a powerful puncher as Dubois, it shows Usyk is rightfully the undisputed heavyweight champion.
When it comes to Parker, if the fight between Usyk and Parker does finally go ahead as per WBO mandatory rules then even if Usyk wins he will not have an easy fight. Parker is definitely a boxer who is not scared or intimidated:
HEAVYWEIGHT BOXING: USYK vs PARKER It seemed to me that Usyk was not worried at all about controlling the center of the ring, he simply used his advantage in movement to score points and make Dubois get tired. Dubois could not press Usyk to the ropes or pin him in the corner, since he always easily escaped under Dubois' left hand. In fact, it is not clear at all what Dubois' plan was (if we discard the most obvious theory - he was beaten but got a lot of money), he showed literally nothing (although of course this is Usyk's merit).