There is the wise old sage, however, and there's deus ex machina. Merlin was a wise old sage. What he does for Arthur is provide information, learning, advice. He doesn't jump around with the knights and throw fireballs. His biggest, most impressive power is to change shape - not to mention one of the only powers he uses. Oh, and he's the antichrist.
Huh? I don't think that I've encountered that trope before.
What about Gandalf? Again, we don't actually see a lot of magic from the old guy. He makes fireworks and creates choo choo train noises and casts Light a lot. Oh, and he's the archangel Gabriel.
Well, more likely just an ordinarry angel. The Valar would be like archangels, I suppose. But I take your point; he wasn't just a man.
However, if you go back and read Hobbit & LotR again, I think you'll see that he does do more magic things that you may have noticed at first. E.g., when Gandalf is opposing a Ringwaith outside of Minas Tirith, and the sun seems to shine more brightly , and people's morale improves - I suppose that to be Gandalf doing magic.
There's been a few attempts from the start to patch up the discrepency. Magic items were a big one. The assumption goes: "Magic is everything in the game that is strong, including the strongest baddies. We have classes that do not have magic. Therefor, they should have magic items."
This was the birth of the Christmas Tree problem.
See, I don't buy that it's a 3e-ism. It's always been there. I'm literally playing a 2e game as I type this (thus the slowness, sorry

), and I deny the idea that characters didn't need magic item. Our fighter needs magical weapons to even harm many baddies, for starters. In fact, if you look through the books, as others have mentioned, most magic items are either intended for fighters or, in fact, are only usable by fighters. The intent is somewhat clear - wizards have magic, fighters have magic items.
I can't really speak to the 3E version of this, but I can to the 1E version. I have to disagree that magic items are a neccesity for the 1E fighter. Its true that a lot of creatures in 1E needed some degree of magic weapons to hit, but most (not all) could also be hit by some nonmagical material. All demons (including princes) could be hit by cold iron. All devils (on down to Asmodeus) could be hit with silver, as could all lycanthropes. Most undead could also be hit with silver. So a magic weapon isn't necessarily essential to a fighter in 1E.
In terms of items only usable by fighters - there aren't that many. Magic swords are an example, and a few oddities. There are probably more items only an MU can use (e.g. many of the wands). Since AC and hit bonuses aren't open-ended, a fighter doesn't need magic armor to survive a fight against tough opponents. A non-magical AC of 0(=3E AC 20) is possible with non-magical armor. If the fighter has a high Dexterity, thats AC -4 (AC 24). Even the highest line on the DMG attack matrix for monsters needs an 11 to hit that.
Likewise, the best AC possible is -10(AC 30). The most skilled fighter hits that with a 14. Add in weapon specialization and STR bonuses, and he could only need an 8.
All that said, a high level 1E fighter still wants magic items and likely will have them! He's just not helpless without them, except vs. a few opponents (e.g. a lich).
As for "changing the world" outside of combat, a 1E magic user is much less capable of that. For example, he can't create his own demiplane - ever. He will likely know very few spells at start, and will be lucky to know the
sleep spell. Versitlity is limited by the spells that you know. Some spells will not be understandable, others will be unavailable.
And many classes can found a stronghold when they reach name level. The one that's best at it - the fighter. Isn't founding a barony - perhaps, eventually, a kingdom - "changing the wordl"?