Major IDs change

Random idea I had, but instead of Major IDs being stuck on an item that isn't good, maybe make it so you unlock them after quest or some trials, and you can then apply like 1 to your accessories, 1 to your armor and 1 to your weapon max (so 3 in total), in exchange of some stat. Like you could apply the Greed Major IDs in exchange of halving the SP you get from your accessories, or get Cavalryman in exchange of reducing the bonus Main Damage and Main Damage Percent you get on your armor

 

hell no

 

To put it somewhat more politely, buffing major IDs seems a bit absurd, given that a lot of major IDs are incredibly strong and the items they're on are designed specifically to address this. The lack of limitations imposed by this would allow some absurdly strong builds, unless the downsides were similarly massive. Even then, it's would still be difficult to ensure this didn't allow some pretty broken builds. By having the IDs tied to items, they're able to nerf your entire build in a way that allows them to control more than just one specific stat change. By requiring you to use an item with built-in downsides, they not only give you the downsides, but it takes one slot away that you could otherwise use to mitigate said downsides. The only way to ensure they wouldn't be broken without this is to design penalities with similar levels of severity to their power, which would probably put most players off of using them altogether.

Take for instance Time Rift. Time Rift encourages a specific playstyle while simultaneously setting a near requirement to use other gear to compensate for its downsides. You are virtually required to have several other pieces of mana regen/mana steal gear to compensate for its penalty; this prevents you from easily stacking damage. It also has an incredibly high intelligence requirement, so you need some stat boosting gear just to wear it, and it limits the skill points you can use in offensive and defensive skills. How would this be balanced without those downsides? Negative mana regen/steal? Well, since you're given an extra slot, you can easily fit a ton of either into your build. Double it? Well, you still don't have the intel requirement, so no stat-boosting gear is needed, you can assign way more skill points into other stats, and you can drop it onto a zero intel build that's purely damage focused, allowing for some pretty crazy damage. Add an intel requirement? Well, you've still got the chestplate spot free to give intel, so it's still easier. Well now we're basically where we started, but with a bit less spell damage, but since you can put something with a damage bonus for your chestplate... It was clearly designed to balance out how strong the major ID was, and they carefully considered how they could allow it to work as intended and be strong, but not allow it to totally run away in terms of power. It would be difficult to do this without having specific requirements and downsides that are similar to those the items the major IDs are already on, in which case, why not just stick with those?

 

Additionally, MIDs like Magnet would be broken with the Jester Set. However. You can only use Magnet with Vindicator or Gravity. Vindicator prevents 4/4 set bonus, while Gravity blocks out Jingling Jester, one of three items with the Greed MID. In order to use full Jester Set + Magnet + Greed, you need to be an Assassin just to use The Exploited, and you need Gravity. And like Melkor said, this would be broken if the items had no limitations

Moving on to the next bit: Fun! (& Synergy.)
Lots and lots of Major IDs are a bit silly. (Take Deadweight.) Or they exist to give early-game weapons a buff and a splash of uniqueness. (Take Overreach, Hesperium, or Roiling Ruckus.) Mythic MIDs already come on Mythics and tend to be less silly. (Take Transcendence, Roving Assassin, or Gravity Well.) In this scenario, you're already using a powerful weapon with the Major ID, while Roiling Ruckus-like weapons are sillier (but much harder to balance). In Roiling Ruckus's case, it's built around Acrobat's Death by a Thousand Papercuts Playstyle. Using Weightless and Flow State, you can basically sustain mana infinitely and get Flow State within one second consistently. Transcendence and Sorcery are just flat buffs that simply can't be represented without MIDs.
'Bad items' can be used to refer to ones that are decent but don't do a lot (Rewind) or ones considered by the community to be bad (Roiling Ruckus). Calling all items with Major IDs bad is just flat out wrong. (Weathered is used by Acrobats in spite of its own Major ID not helping in any way.)

And lastly: Uniqueness.
If your suggestion were to be implemented, then basically all of these wacky Fableds, some Mythics, and some Legendaries would lose almost all of their uniqueness. Most of the time, regular IDs are enough to give an item character and uniqueness. In some cases on high-tier rarity items, the regular IDs are a bit more boring in exchange for something wacky.

Basically, your suggestion would break balance, remove fun MID building, and destroying almost every Major ID-ed item's own uniqueness.