That's the point - If you bring someone in at the wrong level (higher comp = higher level) then you have a major problem.
Compensation does vary within a role, though. Even at organizations that publicly share salary info there is often a wide range within each band and the salary bands may overlap.
Paying everyone in perfect lock-step with each other sounds great in theory, but you end up either paying significantly more than you need to or locking yourself out of otherwise great hires that were just a few thousand short of your fixed salary. Obviously, not everyone within a role performs exactly the same.