I think a major point that's missed here is how XP is awarded. In 1st Edition, XP was awarded for gaining wealth, not defeating enemies in combat. How you awarded XP changed in almost every edition, each time shifting more towards XP for defeating monsters through physical prowess. You can't overstate how profound this change is. How you reward play in your game heavily influences that play.
I played 1E back when it was just "AD&D." And the game was played mostly the way it is today -- TSR's modules (and Judges Guild, for that matter) were almost entirely about "go to this place, stick a sword in these people, go through their pockets." Yeah, there was a bit more of stealing everything that wasn't nailed down (unless the nails looked valuable, in which case, we took those too). The Secret of Bone Hill turned out to be that robbing the town was as productive as fighting the monsters -- the same went for the Village of Hommlett.
But playing a magic-user back then still primarily meant "I cower in the back while the fighter does all the work."
I played magic-users back then, and it mostly sucked, and most people I knew didn't do it more than once, because "I cower" is a really unsatisfying thing to announce each turn. None of my friends read Jack Vance. They certainly didn't go into AD&D thinking, "whoa, I hope I can cower and indulge in clever wordplay instead of actually fighting!"
Yeah, the XP system did encourage a lot of us to make thieves and rob NPCs blind, but most adventures were still about combat, and until magic-users took over the game around the time they got
fireball, no one wanted to play them.
Furthermore, in 1st edition all the classes were not combat specialist. Indeed, the only combat specialist was the Fighter. Wizards, Theives, and Clerics all shined, but they shined in different ways. Fighters were brought along in case the other three classes failed and you needed some meat to throw in front of the ogre.
I killed Lolth in Q1 with my cleric. They were pretty damned potent.
You shouldn't bear the mark of Cain because of this (but you should check out Mage and World of Darkness for alternate magic systems).
Mark Rein*Hagen's voice hadn't changed at the time people were originally playing AD&D. There was no other game in town for people who wanted to be more wizardly.
And "hey, if you're not having fun, it's your fault" is a pretty lame attitude, and one that smart game designers don't indulge in. Given the amount of playtesting 3E went through, I suspect they heard from a lot of people that announcing "I cower again" sucked and changed 3E wizards as a result.