Talents then.
Point is that if you tie and ability t a covenant, and then make changing the covenant trivial then all you have done is make a needlessly convoluted talent system.
Variety is important, but not really to the level where you need to be so obtuse about it.
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It was not all brainless grinding. The Renown armor was the closest, but you had unique armor aquisitions through the Ember court, Sitching Yard, Queen's Garden, and Path fo Ascension.
Make one cosmetic set for each covenant similar to the covenant armor in 9.1, then tie it to a unique method of gathering like the aforementioned covenant minigames, make all covenants (or dragonflights I guess) available without the need to swap, and then have the remaining zone buffs and a few unique mounts scattered around the zone, and you have what I think is the ideal version of covenants.
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You also had the hidden 4th armor tint that was somewhat fun for each covenant (mostly Ember Court).