Borrowed power isn't a problem in itself, the problem is more that these is a complete absence of non-borrowed power. The proper balance is giving players new exciting abilities every expansion & taking away the underused ones.
Bringing back a ton of nostalgic abilities in Shadowlands was a bad idea. Right now it seems they're in the opposite mindset, we've already seen a ton of completely new dragonflight abilities disappear before it even comes out. Priest had a ton of new active abilities revealed & they're already gone. Just to bring back Shadow Covenant? Boo.