I am at the max salary band for my position. His position can admit a higher salary band. After a few years, he’ll have a track record proving his competence in the new position and can apply to be raised to a higher band.

I believe the theory is to avoid the Peter principle. If someone is promoted into a position for which they are not competent, then they can be transferred back to their old position without lowering their salary (since it’s been the same salary the whole time). I also think there’s some stuff about passion, grit, and drive that’s been imported from the private sector.

Differing skillsets? Managing people doesn't have to mean more responsibility. Some people are good at doing, others are good at the bureaucracy game and buffering for the doers. Both are critical, and in a good org, both have different, but not necessarily differing scales of responsibility.