There are 5 possible ranks...why should someone with the middle rank be able to promote? It just doesn't make much sense to me to allow that; yay, you can promote from rank 5 to rank 4! Why?
I have 9 ranks, and could have added more.

All ranks can invite (even the 9th rank). Only the first two ranks can promote. Only the first 3 ranks can kick. And only the first two ranks can set permissions (they have identical permissions, lead and co-lead). Only the first two ranks can withdraw gil. And all but the lowest can deposit items or gil.

Officers (the 3rd rank) can play with actions (buy, use, discard) and modify company board. And that's about it. The 5th and 6th rank are longtime contributors who proved their value. The 4th rank is a "recruitment officer". The 7th rank is where people go by default after 2 days of activity. The 8th rank is AWAY for people planning to not be there a while, no privileges except invite. The 9th is the default for new people, no privileges except invite.