I wouldn't go as far as to say that the key word is trivia and tbh the things you mentioned (item and skill builds) are actually quite static and you can even just follow a guide if you want. I think you are putting too much emphasis on the reflex-based combat at the detriment of the more general "macromanagement" things like predicting the position of the opponents, managing resource aquisition, etc. I'd say that Dota is much more like an RTS without worker units and base building than it is an FPS where each round takes 30 minutes.

Not to say that there isn't a fair share of unintuitive things. A good example is how even though the objective of the game is destroy the enemy base most of the times a team will avoid attacking the enemy buildings until the very end of the game.