Regarding recruitable H4 priests. If the price would be high enough and they would be capital only, there wouldn't perhaps be such a balance problem (I believe Fanaticism is at its highest value in the early phases of the game).
IIRC in CBM C'tis priests cost currently H1 $35, H2 $100, H3 $260 and they all are recruitable everywhere. If the "new" paths and costs could be for example H2 $80, H3 $260, H4 $600 and make the H4 one capital only, then I don't believe there would be at least a very massive balance issue
