I see 6, maybe 7.
Regardless, some are more adaptable than others and would flourish in multiple offensive systems. Some need the right system.
For example: Mac Jones. Mac would be a very good QB in the Sean Payton type system...The system requires an adequate arm (not overpowering) with very good accuracy and a good bit of smarts for all the verbage and play-reads that happens in the huddle and on the line of scrimmage. There are some systems Mac just wouldn't do well in.
I think in the near future, we're going to see the NFL move a lot closer to the college RPO game. Then, I think we'll see them move away from it, as QB careers become much shorter, due to the pounding those guys get.