The WoW Team in the last 6 years has gained an unhealthy obsession with adding in more external systems to your gameplay. Now, there is nothing wrong with an expansion feature in itself (discard thoughts of a well-thought out progression loop, fun design and all that jazz for now), however, the most important thing when it comes to designing these systems is if you balance classes around those systems.
Lets take an example from the old days. We always had set bonuses in the game, they were a fantastic way of adding a little bit extra borrowed power while also showcasing class uniqueness, however, set bonuses (until a certain point, I believe Mists?) were never extreme gamechangers (of course there are a couple outliers, such as T10 Ret pala bonus for DS cooldown reset or T13 tank AoE Shieldwalls). Some set bonuses were really just as simple as giving you a bunch of extra resillience, increasing the dmg on a skill or two, extending the duration of a bleed effect, simple effects that made your class play better but are not over the top, you could easily live without them.
However, since Legion, an obsession developed with super lenghty borrowed power grinds that are a nightmare to progress through (daily 6 hours in Maw of Souls or Island Expeditions) and increase the potency of your class / spec in ways that are simply too powerful to give up. These increases are also staggered over time, so each day or week, there is a new bonus that is in the game.
Because the gains are staggered over time, it becomes impossible to balance. Lets say Ret Pala is doing a bit too much damage than intended in PvP, so lets nerf Templar’s damage by 10% and Wake of Ashes by 5%. But oh, look! Next week, everyone gets a 4% stamina bonus and 3% versatility. Suddenly, Ret now does nowhere near enough damage to justify playing it, because not only did they get hit by a dmg nerf bat, everyone else also got tankier, while they still need to wait 4 weeks for their insane Flash of Light bonus to activate, so they are not even worth picking for side-healing. So let’s fix it then, let’s add a bit more dmg to Ret again!
But, oh wait, next week is coming! New big strength proc ends up scaling too well on Ret pala, so the buff we introduced to offset the tankiness everyone else got is now totally redundant and made Ret too overpowered again, so we have to nerf again.
The game is LITTERED with issues like this since Legion. It’s an absolute nightmare to balance. Rogue Mage in 2s was totally useless in the first few weeks S1 of SL because mages did not yet have the slow effect on their incap and disorient effects from Night Fae (I know they were never bad, I just play a Paladin so RM is easy to beat. Also the slow is still bugged, Freedom or Bubble even doesn’t completely remove the slow…). Suddenly, they get the slow, and their performance skyrockets. So lets nerf Triune Ward. Doesn’t matter too much when people cant hit you though, does it? Triune Ward stays just as obnoxious as before.
BfA. Let’s start giganerfing all the good Azerite traits, and launch 8.2 with Vision of Perfection being a thing. Suddenly, an Azerite trait (Light’s Decree) that wasn’t touched prior to this because people only used 1 stack of it to extend Wings duration is now gigaop and has to be nerfed. Ends up being nerfed. But who cares now that 8.3 is coming and we got a bunch of corruptions that scale out of this world ( ͡° ͜ʖ ͡°) Oh, also because of all the haste corruptions, you have to nerf Death Strike healing, but forget to revert the nerf till 9.1 lands, essentially leaving DK selfhealing in the dust for the duration.
STOP. Create the class for the expansion, and just keep tuning it until a new expansion is coming out. If you want to do borrowed power, do something small like set bonuses or glyphs back in the day, offering small minimal modifiers that make you slightly stronger or make the class play slightly better. You are wasting too many resources by reinventing the wheel instead of fixing the wheel. Every patch and every week while we’re still advancing in the borrowed power grind loop, it feels like classes play totally different, and they’re impossible to balance properly.
The reason why this is so bad is not only are the grinds and systems you come up with have been mostly poorly received from both casual and hardcore players, you keep wasting energy on something that is gone by either the next patch or the next expansion. Where is my Heart of Azeroth (Vision of Perfection in particular)? Where is my Corrupted gear? Where is my Ashbringer? Where is my Soul of the Highlord? Where is my 330% Ret Mastery build from BfA? Where is my Azerite gear? You see what I mean? These are all things that took insane amounts of time to develop, and are discarded without a second thought! It’s infuriating to see this. And next expansion I’m already guaranteeing that you guys are thinking of discarding Covenants, SL leggos, Shards of Dom, conduits, soulbinds, everything that you spent so much time working on in favor of something “”""“new”"""".
My point is: if you design a class, design the class and not an elaborate system that is only good for wasting your own time and money. If you want to have external systems, have them be super small. If you’re a level60 paladin, you should play like you are a lvl60 paladin, instead of playing like you’re 4 expansions ahead if you did the grind.
The philosophy of creating something that is easy to maintain also covers old content. There is no point in going back to do old raids at the most challenging difficulty other than cosmetics, and those old raids just turn into a “lets blindly run through the entire thing” instead of something challenging and as a conduit to experience old lore. Although you are experiencing the issue of having an expansion feature appear 2 expansions later with Mage Tower being a thing right now…
Imagine if you could fight Heroic Ragnaros again without having to specifically create a level appropriate character. Imagine if fighting Ragnaros that way would give more loot than clearing it as we do right now. Imagine all the content that people could experience. The completionism grind.
I did go a bit off track, so as a tl;dr: make things simple for yourselves. Don’t waste time, money and energy on something that won’t live past the next week, let alone the next patch or expansion.