The tl;dr: Aethervision was created as a talent to replace a “core mechanic” that arcane mages have had for probably at least a decade, but instead of just replacing that mechanic, they decided to make it do that mechanic “and then some,” causing complications to the flow of the spec.
Arcane mages had a spell-queueing interaction that could cause multiple spells to benefit from a proc that, as written, should only affect one (commonly referred to as “double-dipping”). It wasn’t intuitive for new players (because it’s not a concept that’s explained in-game anywhere) but it’s very easy to understand once you read or are told about it. Blizzard decided they don’t like double-dipping anymore (but only for arcane mages). They tried to remove it in Beta. The community was furious (this was about halfway through the beta - the number of posts in the mage feedback thread more than doubled overnight). Blizzard reverted the change and promised to “address it with something acceptable at a later date.”
In the anniversary patch, the double-dipping was removed (again) and Aethervision was created to replace it. Instead of something as simple as “allows you to double dip for these specific interactions,” they created a buff that stacks, refunds charges, and lasts long enough to be used in concert with other buffs. This is - quite blatantly - more than what the original interaction was doing.
The immediate response from the community is that it’s bad and disliked. People don’t enjoy playing around it and it makes the rotation more complex (something they promised multiple times to reduce) and less enjoyable. It probably didn’t help that we also received some hefty nerfs alongside the change, meaning that in order to do as much damage as we were before the change, we’d need to optimize our usage of the new talent. As Porom points out, Aethervision creates a rather absurd set of cases for deciding exactly when to or not cast arcane barrage that are considered to be significantly less intuitive than the concept of double-dipping was in the first place. So in order to keep up with what we were doing pre-change, we basically had to create some complex weakauras to tell us how to be optimal.
Blizzard’s response to that feedback was:
And thus you are caught up. The community is unhappy and Aethervision creates a complex number of variables to consider when casting Arcane Barrage - something that is directly counter to Blizzard’s stated goals and opinions.
But honestly, Blizzard could win back a lot of points if all they did was revert Aethervision and give the double-dipping back. They might need to do some numbers tunings to compensate for some of the losses / nerfs, but pre-Aethervision arcane was the most fun I’ve had playing arcane since legion. The fact that they changed it because someone finally realized that an interaction that’s been around for 10+ exists feels like a slap in the face to a lot of us.