The 1e MU only does this if they find the right treasure, just as the fighter only lops of heads if they find the right treasure.
This is not true. The MU starts off with a spellbook. No need for additional treasure to case reality-altering magic. And after name level, they can
make their own magical items. Also, the fighter is still effective without a single magic item.
Yeah, it's a serious question! Because how "magical" something is can be a moving target. If using an explicitly magical sword every round is less magical than turning invisible, once, then we've got some handy guidelines to the aesthetics of magic.
I think your premise is absurd to claim the fighter is just as magical as the MU, and I think the rules clearly show why that's absurd. For one, the fighter class itself isn't magical. The MU is. By definition. As part of the core class. Secondly, even if we ignore that, the fighter is still effective without any magic use at all. The MU is not. The MU has to use magic. Thirdly, you mentioned how fighters can use a ton of magic items that no other class can (which is false), but seem to forget how MUs can use even more that other classes can't*. Fifthly, the magic items a fighter does use are 95% just adding better to hit or more average damage. None of that is reality-bending like turning invisible, teleporting, shapechanging, charming, conjuring, etc. etc. that a MU does in every encounter.
It's simply absurd to claim that the 1e fighter is just as magical as the MU, even if you think the definition of "magical" is a moving target. They are already so far apart from the start that even if you allow movement, they will never come close to being equivalent. Aesthetics are completely irrelevant when the result is comparing a reality-altering effect against a +x bonus to hit and damage. That's not aesthetics, that
effect that are massively different.
*
There are many powerful items of magic which only this class of character
can employ. Most magic scrolls, wands, staves, and many of the
miscellaneous items of magic are usable only by this class.