Balance of power quest implementation is one of the worst ideas from a conceptual standpoint that I've ever seen, up there with this expansion's implementation of Archaeology. Its like they were trying to do everything as poorly as possible.
You have this artifact, with very limited total number of appearances. Lets make one of them gated at baseline behind an introductory raid Normal mode (or higher) only. But not only that, lets make it take 6-8 weeks of doing the raid to get all the drops, then you have to go to the next raid to finish up. Should we make it account wide? No way! Of course you will want to do 6-8 weeks of EN on every character you play! Starting to play a character in patch 7.3 when WQs give better rewards than EN? Sucks to be you! No way you'll be able to find 6 weeks worth of EN groups easily! Guess that one appearance of the 6 total you can choose from (with 2 of those 6 being basically the baseline ones) is locked forever! Oh you did something impressive and difficult like clearing a Mythic +15 in the time limit? Too bad so sad, no appearance for you!
Like I've always said, if you're gonna make something "for raiders" at least commit to it. Make it Mythic raiding only. Normal EN is no harder than LFR EN, but it takes way more effort to do and in the future will be super irrelevant and almost impossible to find groups for. There's no "skill" basis they've locked this appearance behind, only a tedious and arbitrary requirement.
The part where you're forced to have the base appearance in order to use any of them is the only part that I'm really bothered by. Each unlock should be entirely independent and only require you to complete whatever the objective is. Aside from that I'm ok with having questlines and rewards that encourage you to be there when the content is relevant.