Bonjour,
So after reading the current ranking and request system it looks to me that everyone atm needs to write on average, 20 D rank requests for E ranks rank up to D rank, a minimum of 15 C rank requests to get to C rank exclude the potential for doing higher ranking requests, so just in my personal opinion that's a lot of not only write in terms of missions and in terms of grading and i just suggest to either significantly reduce the number of requests by reducing exp requirements or increasing experience received per missions. Another thing that i need to point out is the tiny difference between E rank and D rank in the first place with E rank primarily just having 10 less spell slots than the D rank, whilst everything i've read pretty much stays the same unless i'm mistaken.
Oh well that's enough for my ramblings for now, but i just thought i'd give my input.