I think the whole essence system is complete garbage.
1) They don't tie up with classes or specs(other than 2 of them that are specifically made, but even then 1 of them is a copy+paste for all specs) in any way. They are random stuff and I can mostly compare them to the WoD Garrison abilities in each zone. New random button that does something, but has no ties to your class design.
2) They just seem overbloated with text in tooltips. I try to read what they do and they have 4-5 lines of text of describing some bland effect that again going back to point #1, have nothing to do with our specs.
3) Balancing these will be a nightmare, I can already dread the hotfixes coming "X Essence now does 10% less damage for Arcane Mages, Y Essence now does 5% more healing for Mistweaver Monks". And most likely what is going to happen is that the CD specific one that ties to your spec somehow is going to be the best for a lot of specs simply because it has the best synergy with your abilities and stats(most of them won't scale with Haste nor Mastery of your spec, so if you aim for those 2 stats, you are getting fuck all value from them vs. specs that go for Crit/Vers). Not to mention the possibility of them just saying "fuck it" and not touching them at all, creating a bland "you use these as an Assasination Rogue and nothing else" situation.
4) The Spec specific ones. Particularly the one that ties into a spec's core cooldown ability. This is going to be such a mess from gameplay design and the spec's feel. Very early into the PTR people were reporting uptimes of extremely strong abilities like Incarnation or Metamorphosis to be +80%. It switches up the meaning of cooldowns, instead of feeling good when you use them, it now feels absolute ass when you don't have it up since the time you have it up would be greater than not having it up.
5) Not focusing on problems of the already existing system before introducing a new system that creates even more issues. Many specs are in shambles still, talents are an absolute shit show with no balance changes in the horizon for the rest of the expansion.
Legion talent system of apples vs oranges worked out a lot better. It created a literal meaningful choice. Do I want to go full AoE build, full single-target, or do I want some AoE because it works very well for the fight. Current talent in BfA there is no choice, you take 1 talent that is best in all situations outside of very few niche cases.
But speaking from the PoV of a Hunter, I was changing talents every farm/progress raid, both BM and MM had a ton of talent choices between the two that I could pick and choose to fit the fight with AoE or ST priorities. Now in BfA, I have not used a tome of clear mind for MM a single fucking time. I play the same fucking talents for every single piece of content I do. And same was for BM in Uldir. Which system was better class design?