The player's skill effects as known is sometimes quite overtuned: Obscure the animations and sometimes visions.

The Effect opacity setting do helps alot, but they also lower some of the world's visual effects and all monsters' visual effects.

The point I want to make here is while the player skills vfx are straight up obnoxious sometimes, the monsters and world's vfx are really fine-tuned in my opinion and also have pleasing minute details. It is hard to find the perfect middle point when they both tied to only one slider setting. It should only affect player skill vfx in the first place.

Here's a comparison between 30% and 100%. Should have find some more, but you got the idea. It applies to all mobs and bosses, subtle ambience vfx in boss rooms, the wells' anomaly effect in Magnus questline,..

The following idea might be irrelevant, but let the player customize their skill vfx could be a good solution also.