I'd say you're painting with a mighty broad brush here, and one that's certainly not universally accurate.
And in other news, the sky is blue and water is wet...
If you look at the adventure modules of the era, there was the expectation of frequent combat, and combat at any significant level was not over in a flash.
Beyond that, I'd say that quick combat does not mean that being ineffective for most of the experience is something to be sought after.
Sure, if your whole game is about combat, like 4E. I'm saying because B/X and AD&D wasn't about combat, it was about exploration, not having something flashy to do in every round of combat wasn't a big deal. There were other aspects of the game where you did shine.
And, this is how classes were "balanced" in old school D&D: each had something to do in a certain aspect of the adventure. Not because everyone had the same DPR or whatever...
And as for your observation about 4E combat, I'll just say that 1.5 hour combats are not the norm for an experienced group.
I played 4E for two years straight. We were pretty experienced, intelligent and even made accommodations to speed things up (power cards, time limits, extra damage, etc.) and combat STILL took forever. Nearly every single combat. There are dozens of threads on ENWorld about this very topic. The designers specifically made combat last longer so that the cool neat powers and combos could develop.
To try and blow this aspect of 4E off is just disingenuous.
I played a variant of old school D&D recently (it was Labyrinth Lord) with a mix of young and old players and I can definitely say that low level wizards were not popular. The young players said "that's it?" for what a wizard could do, and the older players reminisced about our spellpoint systems...
That sort of rule is definitely not the way to go in the next edition...
First, I never said that's the way it should go. Secondly, do I care what some kid, who probably sucks at the game anyways, thinks about it? If they couldn't think of anything to do, that's an issue with their imagination, not the rules. The Fighter or Thief have about the same stuff "to do" as a Magic-User, and you aren't here complaining about them. The Thief is arguably even worse off: d4 HD, poor weapon and armor selection, skills are very hard to get success on, etc.
But, guess what, people didn't play the Thief because it had a list of "something to do" on their character sheet every round. They played it because it was a challenging class that required you to use your imagination to survive and finally get powerful with. The same is true for Magic-Users.
Now, whether that's the direction for 5E? I don't know. I never said it should be. Maybe that's not for the Now Generation. Maybe they don't want to use their wits to survive in the game. Maybe they want a toolbar on their sheet with "hit stuff - make magical effect" buttons and cut scenes that skip from cool, balanced, exciting combat to combat.
And, that's fine. That can be fun.
But, for a lot of people, that's not D&D. For some people, D&D isn't about set-piece encounters, balanced combat, or flash-bang-whiz powers each round for everyone.
In sum, you certainly might not appreciate B/x or AD&D if you come at it expecting 4E-style gratification and playstyle. But, if you come at it with different expectations and goals, then you might just find some merit in the 1 spell a day 1st-level Magic-User (and what that means in the grand scheme).