Context matters, some skills keep up with the times and some don't. Some are just band-aided.

Fey Union was created at a time when raid bosses actually can critical hit a player, that no longer happens anymore. Damage post-SB went to predictable ranges at all times going forward and that has also dampened usage of the skill. Removal of Embrace target allowed the creation of the skill, along with "higher" potency on a resource.

Dissipate is okay, the free resummon change made it more worthwhile. Was created at a time when we had Eos and Selene did different things and the skill was also used to strategically swap. We did a lot of Selene Fey Wind into Eos things in HW. I don't even want to remember when it was part of a optimized pull. Shadowflare where the boss will be pulled, hit Fey Wind, and 5s before pull re-summon into Eos. Everything was more complicated than it was now.

A lot of casual players didn't seem to grasp the idea that once you have fairy skills on cooldown, a lot of down periods can just eat up the fairy for the renewed Aetherflow and heal spell buff. Or before Living Dead change, you'd just use up whatever Aetherflow you had and then eat fairy to get more to heal walking dead and move on. Game changer if party mitigation button is missed somewhere. Reality is it's benefit has gotten less as expansions gone by with improved skills and changes to Aetherflow. Removal of Aetherflow could just make it generate new gauge or enable re-use of self-skills.

Seraph cannot be permanent because of it's heavy shield and recast, it's meant to be strategically used in a fight timeline. The ability to reapply a pumped shield without a cast is very helpful in savage/ultimate mechanics where heavy damage occurs 2x in a short span. Like E12S diamond dust and oracle enrage, P4S curtain call, DSR dark knight/paladin swords, niddhogg stacks, etc.

The reality is more fight timelines outside of savage/ultimate need to enforce use of buttons. It's the same thing I say that forcing tank to hit a cooldown or die to a tank buster shouldn't be reserved for savage. So it doesn't matter if they keep redrawing the deck on skills if the fight timelines don't get harder in difficulty.