Only 3e and 4e had the magic item treadmill. 1e and 2e did not. Magic items were tied to the power of the game, because they provided XP that increased PC power. Magic weapons were tied to the game, because they were needed in order to be able to even harm creatures of +X or lower. However, the game balance of 1e and 2e didn't really take magic items into consideration. They were pure bonus and if you had a lot of them, you curb stomped monsters.
It still was a Treadmill in 1e and 2e.
If you needed a +1 item by a certain level to deal damage to any extra planar monster, still needed a + 1 item to deal damage to that monster by that level. The only real difference is that it was more of an on off switch. You either couldn't damage the monster at all, it was too strong to fight straight up anway, or you murderized it.
And any monster that didn't have these requirements or automatically in the second or third group.
And this fails to take into consideration the many DMs and tables that don't care if the game is unbalanced by magic items, because lots of magic items can be fun(See @nevin)
That's why I think that the amount of attunement slot should be higher in 3.
And then just have rules and advice in the D. MG about changing the number of ardomin slots or removing the requirement of the two-man slots, and how that changes your game. And what you can do via variant rules, to make up for it.
But what we shouldn't have is having no limit with no Treadmill. And no advice and then, having a bunch of tables where the DM either loads the party up with magic items and complains that they just cream, everything or doesn't give the party magic items and the players complain that the balance is off.
DND should create a stable base about how is designed and how it's published. Then, educate dm's and players on how to adjust the game away from the published standard. Therefore, people are educated on creating different experiences if that's their fun and not complain about the game not working.
"No rules, no advice. No standards" sounds like a bad game design and publication system that will just lead to disaster. And bad press of your game.