He struggled so badly with the size and speed of Aspinall that I can't see him ever being the best in the UFC heavyweight division.
I think he beats Lewis, I'm going GnP rather than a sub (you can't sub Lewis easily), and his wrestling/grappling beats the majority of the UFC's heavyweights - but he's going to need to avoid the mobile monsters in the division.
If he can get a title shot WITHOUT facing Aspinall/Pavlovich/Gane, then he could technically win the belt - but those three run through him.
He probably doesn't need to fight Francis given it feels Ngannou is at the end of his career, and he MIGHT just beat Tai Tuivasa.
Curtis Blaydes is another who gives him massive problems, though.
Can see him cracking the top 5, but getting to the belt seems too low percentage.