Adding new rows of talents, isn’t it supposed to happen anyway with each new addon? I somewhat dislike the way of talents are going to be picked. Back in the days we had 3 trees and could build our “own tree”, more or less, at a specific point of playing, everyone played more likely the same talents. The talent tree has been introduced. I saw recently the pick ratio of talents in pvp, might work for pve as well, most were at 98%, the others are primarly dead talents. Weapons from Legion, Azerite neck from BfA and the Cov trees from SL are working the same, you can choose other options, but they won’t give you a plus, if you don’t play mainstream choices, they punish you either in min/max DPS/Heal w/e or you get blamed at the worst point for picking this talent/row or picking another soulbind. And I don’t see any better chances to balance it for 9.2. Adding an extra Leggo for some classes are even currently way too busted or feel like in comparison to other classes… meh.
So what would be the best way to deal with “borrowed powers” and not just changing the talent tree options? Imho there has to be a huge change at the system itself. The addition of “pvp talents” was a good first step into a direction I am welcoming. Break the trees into more brackets and listen to that, what people are blaming during PTR. Most changes had to happen earlier. If you choose from those brackets, you get a reward/bonus. Most systems are working like this nowadays, or stop thinking in trees and make it like a line, where you unlock specific talents and others get added. A mixture of talents you choose anyway (the above called 98%) and others, which are optional and fine for the own playstyle, as you can do it at the moment with the cov-trees, or as they should working.