One way to balance thrive is to cap the growth potential at +2. In practice, nekkers can go to 3 each, arch spores 3, drowners 4, nekker warrior 6 etc... You could then have a leader whose talent is to increase the cap to 3 or 4, or use cards that have power to expand the cap while on the board. This keep the power creep down while still giving MO comparable 4 and 5 provision cards.
Real world politics have no place here, especially when they are not even remotely on topic. Two posts deleted.
I honestly don't like such artifical limits and prefer it if those cards are balanced in a normal way if possible. And I don't think that normally balancing them is impossible.