They would have to make every ability effectively do the same kind of thing. You have classes where the abilities are simply too different to compare, an actual apples to oranges problem.
For example death knight gets Kyrian=pure single target scaling will only increase single target damage/mitigation
Venthyr=aoe+runic power generation mostly taken for rp gen and therefore will never be the pick for unholy unless it also just outdamages everything
Necrolord=utility for when deathgrip and gorefiends simply isn’t enough. Damage would have to be ridiculously overtuned to be taken for damage.
Nightfae=15% strength/dr all the time for blood and kinda unholy.
In comparison shamans get 4 flavors of do damage and heal or heal and do damage. Which is probably ideal on the covenant scaling side of things but event then it has cases where elemental or enhancement have clear winners.
Kyrian=generally good damage and healing. Positioning makes wonky for pvp
Venthyr=damage and healing based on tuning pushes stacking crit which will not mesh if lava burst becomes meta.
Necrolord=damage for damage and healing for healing also creates combos for all three but the enhancement combo requires alot of work for little reward.
Nightfae=low damage converted to low healing. 3 second channel with shorter range that no shaman wants to deal with.
So basically even if the abilities are redesigned to do the same general things the flaw is that you end up doing different things and different content WILL reward some of these things and punish others. And thats just the case for covenants that generally do the same thing because many of them are pretty out there in their function.