Yes, it would be. We had that in WoD and it was really silly. It reduces the incentive to try higher difficulties because you’ll already have a bunch of gear from it, so killing bosses becomes less satisfying because you end up disenchanting even more of the loot
That doesn’t really solve the issue, because what makes M+ so attractive early on isn’t just the vault (although that certainly helps, with it not requiring you to unlock the loot options at high ilevel by progressing bosses). The absolutely massive incentive currently is the infinite farmability of end-of-dungeon loot. It allowed you to go from 450 to 470+ with absolutely no lockouts this tier. That’s basically heroic ilevel except you’re not limited to 1 kill per boss per week. The difference between doing that and not in a guild that clears heroic week 1 and steps into mythic is easily something to the tune of 10-15 ilevels (our rshaman vs the guys who farmed a ton of M+).
Anyway, I have 2 main areas of feedback regarding M+ and its impact on raiding: reward design and class design. Not going to get into ideas for how to resolve the described issues, despite having some, because that’d be way too much to read and it’s not super relevant.
Reward design:
WoW’s endgame gearing has historically been focused almost entirely around weekly/biweekly lockouts. PvP and raiding both still adhere to this fully via Conquest and raid lockouts respectively. M+ does not. Ever since it was added in Legion, it allowed you to keep running dungeons for as long as you had time/patience/playable keystones, and you’d keep getting rewarded.
The ilevel of those infinitely farmable rewards has typically hovered around heroic raid ilevel. When combined with M+ being incredibly generous with the ilevel you get relative to the difficulty of the content, this makes it very hard for a lot of people to justify raiding, because they could just spend their time doing keys for better gear than they would be getting from raiding.
It also heavily incentivizes spending a ton of time farming M+ early on in the season if you’re a “serious” raider, because doing so lets you kill bosses more easily. Killing bosses more easily means you can kill more of them in the time your raid group is playing, and more bosses killed means you get even more loot, creating a snowball effect. This is an issue of misalignment between “when you get the gear” and “when you want the gear” for raiding, but the reverse is true for actual dedicated M+ play.
For raiding, you want gear ASAP because the way progression/rankings work is that killing bosses the earliest is the goal. However the way “your” loot works is that you’re restricted by weekly lockouts, and by actually killing bosses which costs you progress time which is incredibly inefficient in terms of getting loot.
For M+, the final scoring of your performance is at the very end of the season. What matters is having the most gear at the end of the season for the last few push weeks. So getting a high “guaranteed” baseline ilevel in the first few weeks of the season is mostly irrelevant, as you’ll be gradually pushing key levels over the course of the season anyway.
The quantity of loot also favors M+, which seems counterintuitive as surely the lockout-based source should give more efficient loot. In M+, you get 0.4 items per key per player, in raid you get 0.2 items per boss per player. So in the time you spend capping out your weekly vault, an M+ player should expect to see 3.2 items, while a raider would expect 1.4 (or 1.8 if you full clear the raid). Of course the raid has multiple difficulties, but those vary in ilevel, whereas the M+ player can continue running “heroic ilevel” keys as long as they want.
The weekly vault also favors M+, because it skips the progression step that raiding has to go through. You have the entire loot table available at the same ilevel immediately, giving you access to a variety of weapons, trinkets, jewelry and armor pieces. The ilevel of the weekly vault has also always been unbelievably generous for M+, with mythic raid equivalent coming from keys in the 10-20 range depending on what time period you look at.
Compare this to raiding, where you have a variety of restrictions. First you need to spend time progressing the boss, otherwise the loot won’t show up at all. This means the options in the vault are heavily restricted, particularly early on when it matters the most. Then you need to kill specific numbers of bosses, which can be quite annoying from a social/management perspective on mythic, as you’re simply not able to “fix” somebody’s vault if you run out of bosses on that difficulty This is unlike M+ where you just play more keys, or lower raid difficulties where they can just kill the bosses they missed. This also means you simply can’t cap out your vault with the maximum ilevel during progress, always having a trailing vault slot or 2 at lower ilevel.
I think end-of-dungeon loot being infinitely farmable is something that must be changed, as it’s not healthy for raid and M+ coexisting. It means “serious” raiders outside of dayraiding guilds spend more time running M+ than raiding during early weeks, and it also means that M+ rewards can’t be as targeted or cap out quite as high as raid rewards (without breaking the game even more anyway)
Class design:
This one is not something I really expect to be fixable, but I still think it’s important to point out.
For a spec to function in M+, it needs to do both AoE and ST. You cannot have specs specialized fully into being strong ST tunnelers. That’s a niche specs like Feral, Subtlety, Arcane used to fill. In raid it works because you have enough spots that you can build your comp around big strengths and big weaknesses. In 5man it doesn’t work, everybody needs to be a generalist.
Burst is also very strongly emphasized, because blowing up a big pull before it can kill you is how you save a lot of time. This means specs with flat damage profiles or which require a lot of setup/ramp suffer massively. Examples of this were Shadow, Feral again.
So thanks to M+, we can no longer have heavily specialized specs (ST, low cleave, spread cleave etc), flat/sustained DPS specs, setup/ramping specs. That sucks, because being a specialist and getting to do “your thing” feels great on a raid boss.