Devs should find a way to make "strategic unlocks" as useless as possible.
Part of the fun of the game consists in unlocking things.
There should be more incentives in unlocking, for example: the bank preparation is increased by 1 gold for each 4 classes that completes a level (I just made up the number, it could be 1 per 10 classes).
+1000000! I feel like shouting this out every time I see people seriously discussing "strategic unlocking". The game should NOT support (let alone be balanced around!) that broken style of play. It's just a bad idea to have unlocks that a) are optional, b) are permanent, and c) have permanent downsides...
And like you said, it's easy to fix, if you just gate the hardest content on unlocking all the gods/classes/etc. (ie, remove the "optional" part.)