I don't know what "abuse" means, but if we're talking about me negating the element of randomness, then yes, that's true. For example, it's quite problematic for knights to acquire the desired magic school compared to mages. And so what? Is that a reason to refuse the most useful (for me, useful) skills? Of course not. I systematically develop the hero until all 8 slots for secondary skills are filled. If, for example, earth magic doesn't drop as the last skill, I simply edit the Save Game using Heroes III SaveEditor. Moreover, I don't even consider this cheating, because from my point of view, it's simply a bug that makes further gameplay with that hero meaningless. Should I start the map over? Of course not. That would be silly, wouldn't you agree? It's easier to manually fix this bug and continue enjoying the game.
In principle, I understand the developers' desire to balance heroes of different classes, but in that case, the balance should be achieved not by forcing the use of various secondary skills, but by more carefully working on other possibilities. In other words, fire magic should be just as valuable an acquisition as earth magic. Does the game have that? No. In the game, half of the secondary skills are not used by anyone. Not to mention that some castles are obviously superior to others in terms of troop strength. These are the balance issues that needed to be addressed. And not by taking earth magic away from knights... Heh...