But then it's fair to say what qualifies as disassociated for one person can easily be different for another, right? In other words, it's subjective and therefore handy for describing personal taste but not so handy for objective criticism.
Yes and no. Individual personal tastes aren't completely random; they tend to line up. When a movie is a big hit, the people who like it mostly like it for similar reasons; when a movie is a flop, the people who dislike it mostly dislike it for similar reasons. It can be valuable to examine these reasons - heck, I'd say that this is most of what criticism is. They may not be completely objective, since some people will still differ from the norm, but they're regular enough that it would be improper to dismiss them as subjective. They're
statistical, lying in the border zone between subjectivity and objectivity. Like how we can say "men are taller than women": not universally true by any means, but generally true, a trend.
The upshot of this is that when someone says that they do not think a mechanic is dissociated, we can't say, "No, it totally is, your opinion is wrong" (as long as he's using the word correctly). But we
can look at a mechanic and say, "Most players think this is dissociated, so if we're trying to avoid dissociated mechanics we should probably change it."
I'd also say "control the narrative" is a mutable descriptor as well - couldn't you argue that trips, pulls, pins, grabs, disarms, and certainly death blows 'control the narrative'?
That's a character controlling the environment. When we say a player "controls the narrative" we mean he's dictating things that his character isn't. Like if the rogue had a "Fence" ability that actually put a friendly merchant in a convenient location. The character doesn't have the ability to conjure human beings out of nowhere, but the player does.
I should be clear that there's nothing inherently
wrong with mechanics like this. One of my favorite RPGs, the Fate system, is largely built around them. I'm not condemning them. I'm just trying to explain that there is a real distinction here, and game designers ought to be aware of that distinction in order to maintain a consistent style.
Yes. Hades' Helm of Darkness for concealment, Hermes' winged sandals for flight, and an adamantine sword (a harpe, potentially even the one used to castrate Cronus since it was given by Zeus). The magic wallet might be a particular perspective on the bag given to him to carry Medusa's head in. He was pretty thoroughly decked out, and if all of those items required attunement I suspect he, too would have exceeded the 5e maximum.
Yeah, Perseus was something of a Christmas tree. But as far as epic heroes go he's very unusual in this regard. The only other guy I can think of with multiple magic items is Thor.