Maybe the monks could be made into female monks and placed on tier 4, while all the others are leveled up?

I've already tried that...
Even though it fixes the retraining issue, having 3 archers in a row doesn't look very good, but if it's the only solution... well, I'll have to take the risk.

Regarding the griffins...
It creates a complete imbalance! Some will have to get used to it (or not download it at all).

The problem that disappeared but reappeared: who will be the "?"

Added 8 minutes later
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I have a very raw version ready (no icons, no text, only textures, only balance)! I'm not going to upload it because sometimes people accuse me of being incompetent because of its "rawness" (if you want to test it, write to me in PM).