It's even better than what you describe.

You didn't mention threshold, which further improves on it. More than simply being able to "draw land when you need it" you aren't limited by having to use specific resources at specific times. Threshold ensures that you are able to cast the spell if you have enough mana, while still making those more powerful spells a bit more difficult to cast if you want to run a multi-colored deck. The challenge and thought process is there, without just getting screwed because you drew all green cards but only have one forest and a bunch of islands.