I don't think I can agree with any of you wholeheartedly without more information.
Expanding capacity to hold abilities that have variable cost in lieu of expanding damage is adding value -- you're adding utility or the possibility of generating a stronger combo rather than directly increasing your current damage.
Let me address a few things I've come across in my game-play:
I've also lived without using rain; didn't bother with it at all unless I was being particularly impatient on classic difficulty. I am sure even on the harder difficulties it will be the exact same because there are solutions to everything currently.
Your skills in the current build can shore up the differences from neglecting your primary attribute for quite awhile as well as picking up the right combos along the way or simply having extra abilities to make up for the deficit. All your abilities scale upwards with you anyways and the penalties are to offset that. So you can be several levels behind and still be competitive.
Zone control isn't useless; it can be exploited depending on how much of a scum bag you are or simply it can be used for CCing while reserving your larger spells to deal with more troublesome foes or if you're in an endurance fight it can also help out as well since most of your spells by that point are on cool down depending on your party composition.
If you're interested in gaining more power you're going to need memory one way or another. One shotting Alexander, for example, will probably require you to have more than the baseline memory.
