So in other words, you don't want any assumptions about how many encounters there should be. To me that's kind of like complaining that you took the race car piece in Monopoly and it doesn't go faster than the other pieces.

The way spellcasters work being different than other classes is pretty fundamental to the concept of the game.
They tried balancing things out like you suggest in 4E and it was not well received. To many people (myself included) it did not "feel" like D&D. That's a whole separate topic though, and one I don't have desire to rehash.
But maybe D&D's structure just doesn't work for you, which is fine. No game is going to work for everyone.