And I don't agree. It seems to me that if something is "way too great" at the cost of 50 hours, or 100 hours, that it is just "way too great" period. I don't see how being a full 7 path invoker is more balanced by having them require a lot of tedious, but ultimately not very dangerous investment.

If 7 path invoker is OP, then it is OP. At 50 hours or 150 hours doesn't really change a whole lot, when the bulk of *any* character's natural lifespan is still in front of them. It's not a risk = reward mechanic, just a time = reward mechanic. That time is, generally speaking, not particularly interactive time either. Cast, sleep, eat, drink, repeat.

If it is a case of rarity... stick the limited race restrictions on the class? It feels like there are better solutions than "dump 100 boring hours".