I've actually been feeling the same way. Specifically the level 99 trial, the part with 2 sets of swords flying at the same time gets me almost always. I have trouble checking one side's safe spots, and then checking the other side's safe spots, all before the attack goes off.
And even if these types of mechanics actually have some sort of easy cheesy way to instantly figure out the safe spots... What's the point of it then? What is it actually be challenging you to do after you learn it? Managing your job's uptime, and that's about it I guess. It just looks like more fancier safe spot dancing to me. Is that what passes as a "mechanic" now?
Instead of the game challenging your job and your party's composition, it's challenging your mind's ability to quickly comprehend the pattern. If you can't get it you instantly die.
But, like others said, it's not like the game has anything left for the devs to challenge you on. I think this kind of visual clutter is the epitome of the game's shift in fight design in Shadowbringers. It most definitely became more difficult than Endwalker, but more in the sense of "you have 5 seconds to find the safe spot instead of 10". If this expansion's focal point is encounter design, I was really hoping that they would replace the "find the safe spot" part of encounter design... Otherwise I can't see the difference between here and the last 2 years.
I'd honestly be fine with visual clutter if it was designed in a way that it imitates sporadic damage to random party members. Like a couple of "ow dangit"s that don't immediately stop the raid but recovery's still possible, and encouraged. The closest example I can think of is Barbariccia.
But most of the time visual clutter mechanics instantly kills whoever messed up, then the party gets hit with a body check and the raid has to start all over again. Personally I don't enjoy this "vision" of difficulty. And I think this kind of design is what makes Party Finder less enjoyable for both the person who understands the mechanic and the person who doesn't.
I admit I'm not a fast thinker. Maybe I'm just slow and I have to suck it up. But this isn't the kind of direction I'd enjoy in an RPG with tanks and healers and supports.