my issue with having a lot of major ids on mythics is that it takes away from the identity of the mythic and often can take away from the intended playstyle, or even make it much stronger than it needs to be.
For example we can look at absolution. Does it need a major id? Absolutely not. It is intended for very high heals as a gameplay mechanic. Giving it a major id not only complicates the mythic much more but it also makes it more about the major id than the playstyle its intended for instead
Fableds are a good place for a majority of major ids because they are heavily disconnected from what is generally the intended playstyle of the class. Most go into gimmicks where you build entirely around the major id itself.
Are there some that work? Sure. The nulli major id works very well with the weapon as it is a generally tankish weapon to begin with (high ele defs, reflection, ls, and def). It didnt have much use because assassin in general is usually not a tanky class. This major id rewards the playstyle that would normally be (intended) used with nulli
I generally just dont think that a lot of major ids really fit the current state of mythics, for the sake of balance and what playstyles are generally meant to be used by the mythics