In 3e, the boosts are paced out over a much longer time frame, and that distorts the power curve in some important ways...
Perhaps, but the problems in 3e start happening long before you hit 10th level, and the balance between classes (if we ignore the underpowered thief and monk) was better even after 10th level in 1e than in 3e. And this is true largely regardless of equipment issues, provided everyone has the same level of equipment. Certainly, in my 1e games, the sort of items you mention weren't falling into everyone's hand by 10th level, and PC's couldn't count on optimal kits of belts of giant strength, gauntlets of ogre power, and hammers of thunderbolts, vorpal blades, or holy avengers.
The problems 3e introduced in spellcasting are numerous, and each of them by itself probably isn't wholly breaking, but collectively they are a mess:
a) Changes in the saving throw mechanic: One thing you should note just how much better a 1e Fighter's saving throws are overall at high levels compared to any other class. The fighter improving his save every 2 levels, and continuing to improve it up into the high levels meant that while other classes might have one good save as good or better than a fighter, the fighter was generally the best or second best in every single category - and there were more than three. There is just no comparison in 3e to how good the 1e fighter's saves actually were. It was better than having three good saving throws, because to make the situation even worse, the 3e rules boosted the difficulty of making a saving throw by increasing the DC of the saving throw by the spell level or by 1/2 the HD of the creature (in the case of abilities). In 1e, as a character leveled up, he failed saving throws less and less often - which was essential because as he leveled up he faced more and more 'save or die' effects. But as a consequence of the 3e change, as a character leveled up, he passed saving throws less and less often as saving throw DC's increased faster than saving throw bonuses improved. This meant high level 3e revolved entirely around having absolute defense's to lethal threats - death ward, freedom of action, hero's feast, mind blank, etc - and this in turn meant that while spellcasters were capable of defending themselves, non-spellcasters were wholly reliant on spellcasters.
2) Changes in the ease of casting: In 1e, a spellcaster casting a spell was vulnerable. If hit, the spell would fail. While casting, he could take no other action. The order of action resolution would ensure casters often did get hit while attempting to cast a spell. In 3e, casters only got hit typically if the opponent held an action to counter them, which for most creatures is a losing strategy akin to being debuffed. In theory, the AoO mechanic that formalized related 1e ideas, was supposed to mean a spellcaster was vulnerable in melee, but in practice this never happened because a 5' step generally took the caster out of range without impacting casting, and it was trivially easy to use 'combat casting' to avoid drawing attacks of opportunity at all. These changes made the spellcaster much less reliant on having a meatshield in order to do anything.
3) Less conservative interpretations of spells: One thing that will strike any modern reader of the 1e rules was just how painfully spellcasters were gimped, often in surprising and unpleasant ways. Haste aged you two years every time you used it, ensuring an early death to anyone that used it often. Polymorph Self copied only the external appearance of the creature, and did not even allow you to make attacks while in the alternate form. Polymorph Other transformed the mind as well as the body of the target. Spells were often written with restrictions that would strike the modern reader as perverse. 3e designers harshly gimped spellcaster direct damage, based on well known problems with 1e spells like fireball being too powerful in 1e. But in the case of other classes of spellls, they removed almost all restrictions on their use, often without reevaluating the spell with adequate playtesting. The result was a slew of problematic shapechange, summoning, buffing and debuffing spells that had either been concealed because in 1e you just needed lightning bolt or fireball for most problems, or by their harsh drawbacks.
4) Changes in HD: One of the biggest changes is that after 10th level or so, in 1e you stopped gaining HD. This combined with the fact that fighters no longer got effectively twice the bonus from high strength and high constitution that other classes received, meant that for the first time, spellcasters could manage to acquire enough hit points to survive being one shotted by a peer foe. This was a huge change. In 1e, a M-U's had on average less than 50% of the hit points of a fighter class, and would stop gaining significant hit points at 10th level. In 3e, wizards could get the same large CON bonuses as fighters, and gained HD at every level. Since at high level, CON bonuses vastly outweighed HD in significance, it wasn't unusual to see spellcasters with 60-75% of the hit points of a fighter even before buffs. Indeed, with reduced MAD and point buy, a spellcaster might have a better CON than a fighter.
It was not necessarily considered such a problem that the Wizard outclassed the Fighter in certain important respects when the Fighter could potentially one shot kill with his Sword of Sharpness. Being such a Fighter dangled the carrot of glory and fun, so whether the game was exactly "fair" was adequately forgotten.
I have to strongly disagree with this. This theory is precisely the theory of 'balance' that 3e ultimately ended up adopting. That is, "If something is broken, it doesn't matter if something else is broken too, because if everything is broken it's balanced." And not only is that not true, but merely hitting things with a sword of sharpness because you might kill them is not balanced with the ability to temporarily change the very rules or reality.
Getting back to Celebrim's point, the DM could choose to boost the feats for the martial classes, gauging against the big spells the spellcasters are getting. Or the DM could purposefully sprinkle in "DAMN fun!" magic sword and shields and armor and bows and helms that will boost the fightery classes.
I think you are failing to understand the problem. Once again, the problem in 3e isn't that mainly that fighters aren't good enough at hitting things with sticks, so giving them bigger sticks doesn't help that much. The problem is that fighters are wholly reliant on spellcasters to defend themselves from the threatens that they commonly encounter.
