Joshua can beat Usyk, that is possible but is it likely? As you said, some people said yes and some said no. One thing for sure is that Usyk will not go the same way as Ruiz did when he was focusing more on partying and having fun rather than train heavily with a view to defend his title against Joshua in the re-match.
Dont know it this is really plays a huge difference, but I've read that in Joshua vs Ruiz first fight Joshua weighed unusually a lot, compared to his regular weight. Joshua even said that with extra weight he wanted to be stronger, plus he mentioned that he chased Ruiz instead of cutting corners. As if he was clumsy and used wrong tactics.
During their second fight Joshua was much leaner. If I found correct numbers, he was 12lbs lighter. Is this weight difference significant for a heavyweight ?
Maybe he wanted to move a lot and that's what he did during the second fight with Ruiz. And he won boxing around but there were moments in the fight wherein Ruiz will hit him and you can see that Joshua is still afraid of that one punch that will KO him.
In the Usyk fight though, it was a disaster for him, the plan didn't work or maybe he has a hard time with fighters who has great technical and boxing skills.
Yes, it's was not even close in the first fight. You can see the effect on Joshua's face that he took a beating.