In the past few patches, we got tons of nerfs to keep the balance between classes. That approach - nerfing - Is a bad approach in the long term. Losing something feels twice as bad, as to gaining something feels good.
Example: Would you rather gain 100 dolars, or avoid losing 100 dolars? Most people prefer not losing 100 dolars, despite the end result being the same. Putting this in ESO terms, would you rather gain buffs, or avoid getting nerfed?
Imagine someone getting really invested in a class (Let's say DK), and then you nerf everything they love about DK, until they are as balanced as the other classes (because in this example they were OP). That would feel awful for the DK mains, and the other classes wouldn't feel any better themselves. They would just be able to fight DK now. Instead, if you buffed the other classes to the same level of the DK, everyone would gain from it. DKs would get more fair fights, the other classes mains would feel great, they would gain new tools, new skills to explore, test, and so on. DKs main might test other classes too, etc.
There are so many skills in this game that are underused because they are underpowered. Buff those skills instead of nerfing the OP skills. Seriously. Don't remove a feature from the game (like DK reflecting projectiles), add a risk to it instead. Taking reflect for example, instead of removing the feature enterily, you could've made so that you take 50% of the damage you reflect (you reflected a 5k swallow soul, but you still took 2.5k damage). Reflecting other people's projectiles is fun - But getting your projectile reflected without any counter measure to it's not fun too.
Combat should have risk and reward - Just because a skill is powerful, doesn't mean it's OP. It could be that the other skills are so weak, that the one that everyone is using is the only tool they have. If you nerf that, they are left with unfun skills to play with. A good example of proper balance is DOTA They have tons of OP items, OP ults, hard counters, and etc, that even though certain enemies might seem really strong, you can use this other tool avaliable that also feels really strong to fight against it. You never feel weak or underpowered in that game. That is the good long term approach of balance - having a lot of strong options available to you.
And yes, buffing everything instead of nerfing would bring the powercreep issue, which is already a problem (due to CP, not skills), but honestly? Powercreep is a PvE problem not PvP. You can easily buff PvE monsters if needed, and most skills that are important on PvE are already powerful enough (Blockade, Endless Hail), so that probably wouldn't be that big of an issue. Buff morphs that are never used, buff skills that are never used (Camo hunter, silver shards, fire rune, and so on). Stop nerfing the OP, the fun. Buff the underpowered skills. Give us more options.