First a definition.
Borrowed power, for lack of a better word, are spells and/abilities that contributes to a class performance that are not part of the class itselft. Can be a legendary, a spell that is used in a zone or a covenant ability!
Disclaimer: it is beta, numbers are not final, yadi yada.
Current BFA and Legion have been plagued with systems that were outside a class that contributed a lot to the performance of a class. Such a system is legendaries. The issues with legion’s one have been dealt with in a sense, since getting them in shadowlands will be easier and more targetted. But few problems remains and will determine greatly how your class will perform.
not all classes are equal. Some classes have very high performing legendaries, other classes are left behind and given uninspiring legendaries. Not only outliers will need to be identified but new legendaries should be put in there for some classes.
Lets get this out. Not all covenant abilities are equal and by a large margin. I might be even so bold as to say that some classes will only be able to get good because of it. Yet now, those classes seems ok but their performance rest entirely on a covenant ability. Any nerf to the covenant will severely impact the class.
I feel that BFA has suffered a lot from this disparity. Borrowed power being reponsible for a huge percentage of your performance and not your classn not your mastery of your rotation. The culmination of this are powers the player has zero control on.
We are heading into shadowlands with two potentials issues:
Legendaries and Covenant abilities that are too big a portion of your character performance.
For covenant it is an issue in a world where one cannot easily change covenant and a potential frustrating issue for players: imagine your class performance is only OK because of a covenant or legendary and it gets nerfed: not fun at all.
What are the possible solutions?
I think classes must be designed to perform well outside of these powers. The rotation must be fluid, talents with good synergy and situational talents: all outside any covenant or legendary
Covenant should be utility only and play no direct part in your performance.
Covenant conduit (and gems) should shore up existing strenght of the class and be situational: basically add to aoe or ST or CC or sturdiness or a combination of 2.
There should not be a fire and forget type system that push you to the top, thats bad design.
Legendaries should be there to spice up your rotation as well as push your power in certain situations, without being a fire and forget this-wins-all legendary. Some legendaries can bring utility in various situation, which is fine.
I think we are heading for a balancing nightmare and some classes will find certain specs dead in the water if nothing is done design wise.