Quote from Neospector
You don't absolutely need diamonds for anything except obsidian. You can actually live with iron, and no diamonds. And, no, it does not take a half an hour to get what you want; I once tried getting a helmet with respiration and aqua affinity, but it never came out with those two by themselves. This was in creative mode, using a gold helmet (the highest enchantability), and full level every time. Trust me, the randomness balances out any overpowered stuff the enchantments throw in; you can't somehow get Protection 5 on a diamond armor set and get Fire Aspect and Smite on every diamond sword you throw in there, getting them requires work. It's especially annoying if you get the wrong enchantment, such as getting silk touch on a diamond pickaxe when you don't want silk touch, as then you either have to live with it or throw it out. Enchantments are not a random detail Mojang threw in without balances of any kind.
Considering that it's mostly based on luck, I think it could be argued either way depending on the individual's experience with enchantments. Looking at the other replies, though, I realize that there are people who do not use mob spawners and mob farms as heavily as I do, and breaking the enchantment system would be unfair to those people.
I don't have a proposed solution, but perhaps they could somehow make mob spawners a bit less attractive of an option and make normal gameplay look better? I don't know, just a thought.
( you make good arguments )