I’ll give you a current example that even occurs in 5mans: if you do mythic+ above 10 right now there’s a bonus mini boss that casts both a big white circle on a player (which is very bright) AND smaller white circles of almost the same color that can overlap with the big circle of almost the same color.
Sure: in some cases if you’re ALREADY aware of what is going on with those problems you can avoid them but: that’s a fallacious "solution’ because it doesn’t fix the design problem and it only makes the mechanic harder but in an annoying way because people have to jump around to see.
I think the problem is related to higher difficulties (or more so). They generally do more abilities and the visual designers may mainly care about normal modes.
They might have to think of a reduction-algorithm that does heavy cleaning in some cases (though the op text example is more serious).
Nah, it’s worse when the boss ability has the same visual, or very similar to a player ability, so you keep standing in it. Happened to me a few times and couldn’t find out how I was taking all that dmg