Not really true in 1e. Magic armor is nice, but non-magical armor plus a good Dex can get them into the first steps of negative ACs already. Plus, once you've got magic armor, the ring of protection no longer helps your AC anyway. While still useful for saves, fighter saves really aren't bad at that level. A magic bow would also be nice for the very few flying creatures that need magic weapons to damage, but few of them really have ranged attacks that can pelt the fighters all day. And then, all they have to do is take off 50-75% of the creature's hit points to ground it, letting them bring magic melee weapons to bear.
While it's true that fighters are more gear-oriented than wizards, let's not overstate the dependence.
Not in my experience. At 10 HD, monsters have a THACO of ~10, so if you don't have an AC of at least -5, you get hit a lot. With no cleric to heal you, that is not good.
And IIRC, fighter saves are ~10 as well giving you a 50-50 chance on every effect you run into, again with no neutralize poison, remove curse et al. coming to the rescue. So good saves are a must.
If you play with the numbers, you can actually see that for a fighter after level 9 a +1 sword and a +1 RoP are better than gaining a level. High level fighters are their gear.