Spell "slots" in OSR, Dafter than a brush

I'm going to come out and say it straight up. Spell slots and spell memorisation is absolutely awful. The original D&D and almost every OSR derivative has carried on this nonsense (including my first OSR OSRIC), and as far as I can tell, for no good reason.

Why is it bad? 

It is the opposite of fun. Just think about being that Magic User, at the beginning of the session you pick that spell to memorise and never get to use it. Gosh what sterling quality fun that is! The perfect spell that's needed in the minute...was not memorised, more sterling fun.

It is not good story telling. When a Magic User pulls out the perfect spell at just the right time, you have a story to tell and share. When the Magic User just shrugs in response to a desperate need from the party there's no story there, no exiting flash of fiction to cause gasps and tales over beer in the years to come. It's a nothing burger.

There's no rational reason for it. I've read the original D&D and plenty of other OSR games, and I've never read a rational reason for it. Sure there's some literary inspiration reference in a book I've never read, but what good is that too me? Am I supposed to go read that book in order to enjoy this game? Not going to happen, So within the game, what the heck is the reason for the limitation imposed by slots? There needs to be a world-reason given for it to make sense. To me the whole structure just feels like a mechanical restriction imposed for a non-story reason. I won't argue that its imposed because of "balance" because there is no balancing a 1st Level MU and Fighter. So I see no genuine mechanical reason for it either.

What is better? I'll offer a suggestion here, but it is just one idea. 

Lets start by retaining the restrictions of the power of spell, thus a 1st level MU can still only cast 1st level spells. This restriction make story sense to me, as the character progresses they learn to handle more powerful spells. So lets keep it.

The existing rules allow higher level MUs to cast more spells, so again this makes sense. A MU learning his craft could clearly learn to use their power more efficiently. So lets keep that.

I suggest we add to the above a points system for casting spells. These points will be representative of the amount of spell casting power that that the MU can wield.  

Thus a 1st level spell costs 2 points to cast, and a first level MU has 2 points to spend.

At second level the MU gains 2 more points to spend.

At third level the MU can now cast 2nd level spells. So lets say a second level spell costs 4 points to casts. The MU at third level gets 2 more power points. This allows them to cast three 1st level spells, or a 2nd level spell and a 1st level.

As levels progress the cost of spells by level and the number of power points the caster gains could be adjusted.

So there you have it. An idea for a better spell system that would be more story-friendly and offer more versatility.  I might add that the progression I came up with in this post doesn't have to replicate OD&D exactly, in fact its probably better if it doesn't especially if you are striving for "balance".