I am not familiar with Joseph Parker, but it looks like he did great in his last three fights. But despite that, I don't think he'll be able to beat Usyk. In Usyk's rematch with Dubois this July 19, he showed how dominant he can be in his fight. I have no doubt Usyk will outbox Joseph if they fought.
We can't be too sure about this till the fight happens only then can we find out if Joseph parker can beat Usyk or not. Am a big supporter of Usyk, but I also understand that Usyk cannot be champion forever. At some point he's going to lose unless he retire before then. Joseph parker has been winning his recent matches same as Usyk so you can't completely write off Parker. Parker is also showing some similarities that Usyk was showing back then when he was rising to stardom. Usyk Vs Parker would have been more interesting than what we saw against Dubios.