Since some ‘Imams’ were also military and politicians leaders (at least one according to the lore of the game), they could have a different function than the proposal I have made about priests in general:
Imam: Generates much less experience than priests, but increases infantry creation speed by 1.5% and cavalry by 0.5% when garrisoned in the mosque. (They would not occupy population)
With a limit of 5 possible, then we would have a + 7.5% infantry creation speed, and a + 2.5% cavalry creation speed.
This would solve the problem in the treaty and / or late game. Although I do not see problems if it is used in supremacy because it would be 750 gold in total.
It could also work like this:
The ‘Pallasian intrigue’ card delivers a new exclusive upgrade called ‘Imamate’ for magnets that would grant what I just mentioned above and available in the industrial age. In addition, each imam would accelerate the delivery of troops from the metropolis by 1%.
Without this enhancement the imams will function the same as their European counterparts.
Another possible way to implement them would be:
When they are garrisoned in the mosque they generate experience, and when they are garrisoned in the capitol they increase the rate of training of troops, and accelerate the delivery of military shipments.