Much of how you improve in anything whatsoever is trial and error. That's not saying anything.
My post wasn't very clear. I mean trial and error in the sense of just taking blind guesses, which you often have to do in roguelikes unless you read a guide. It is not entertaining to have to guess how a system works. A much more entertaining challenge is when the system is clearly specified and you have to figure out how to use that system to your advantage. I want to know the rules of a game and then think about how best to play, not spend my time just deducing what the rules are.
I would go as far to say AoD is not difficult, or not challenging in the sense I am trying to convey. It is a more artificial challenge. But the alternative is non-challenge. A typical rpg might give you 5 easy filler encounters, where AoD gives you 1 encounter that you have to reload 5 times trying different guesses. I am being as critical of AoD as I can be and I still can't say it is really any worse than the alternative. Both cases are weak as gameplay but they serve as vehicles for content, which as you say is what matters.