talents have been in the game since launch and every expansion we got a big new shiny end of tree talent and a new ability or 2 while leveling to the max.once they stopped adding skills every expansion they added BORROWED power in an attempt to combat bloat. you get new stuff use it for the expansion then it goes away. this was widely panned for the last several expansions by most of the players and caused wild balance issues when several BORROWED power systems started overlapping
The one positive thing about the borrowed power systems is we have had a few diamonds in the rough over the years and they made it in as talents or shadowlands legendary effects. there isnt a single OP cov ability i can think of off the top of my head. the issue is they are compounded by conduits and then compounded again by a lego and then compounded again by the 2nd lego and then compounded again by the classes cooldowns.
There are a handful of cov abilities that are well designed and fun abilities that fit class themes quite well and there are some that are bland and poorly designed and are getting thrown in the trash where they belong. sepsis is the perfect example. cool spell and fits with the class. the problem is there is a conduit that buffs it an insane amount, then assa mastery, and then 2 set, and then 4 set, and then the shiv conduit, then vanish lego, and then vendetta. no one wants a giga modifier stacked sepsis cheese 1 shot but thats not what we are getting