Unless they've done a complete 180 on Covenant design since the reveal(lol nope). Then they will be the Azerite of Shadowlands.
We all know Blizzard is absolutely awful at balancing. Locking player power behind a choice that should be for cosmetic and story purposes is absolutely moronic.
There will be a BEST Covenant ability for your spec/class. It will be the best by a long margin. There will also be an absolute worst.
Then - nerfs and buffs will happen and the pendulum will swing again. But Blizzard has already said they're going to make it extremely hard to switch Covenants.
Why can't these morons open their eyes?