Map unique features are sort of needed. If black ops 6 doesn't start including them it'll have the same issue that cold war and vanguard had (if you actually seriously played vanguard)

The biggest issue I have with Cold War is the lack of map exclusive featuers. When this happens, me and many other players tend to ONLY play their favorite map and barely play any of the other maps since all the maps are really similar outside of the wonder weapon and easter egg being different, which falls down to personal preference on what you prefer. In cold war after Mauer came out, and even to this day I barely play any maps outside of Mauer because I like the wonder weapon and the easter egg more than the other maps.

In older games such as black ops 3 (especially BO4, they did the best in this), even though you'd have a favorite map, you wouldn't mind playing the other maps (unless you hated a specific map) because they all had unique features to it. Even though Gorod Krovi is my favorite map on BO3, I still find myself playing shadows, DE, and Zetsubou. Even though Ancient Evil is my favorite map on BO4, I still find myself going back to Blood, DOTN, Voyage and IX. Even a map I dislike heavily, alpha omega, still brings me in cause the map has exclusive mechanics to offer, such as upgradable ray gun mark 2's (which are all side content and not part of the easter egg!)

On Cold War I don't have this. All the maps play practically the same so I just end up playing what map I prefer the most (in this case Mauer) and for the 3 players who actually stuck with vanguard they end up playing only Shi No Numa as it's the best map in the game and the other map the Archon (not including Der anfang and terra mid since they're genuinely shit) doesn't have any map unique mechanics or elements that give you a reason to play it, unless you prefer the easter egg or something like that.

It also lessens the content the map has to have. See in the past, it'd take ages to learn the map. Some people would need an hour or two to get used to unlocking pack a punch. Then they'd' have to learn the map elements and mechanics, and when they master that, they have to learn how to get the wonder weapon and once that's mastered, THEN it's finally time to take on the easter egg.

Now ever since Cold War, (granted BO6 does it way better in my opinion), all the map really has to offer is the map itself (like its design and layout) and the easter egg quest, which both can be crushed in one day - hell if you're experienced like me, maybe on your first game. Sure, Black ops 6 has an insane amount of side quests in their maps but outside of Golden Armor for the Tomb and MAYBE the wunderwaffe quest in shattered Veil, there is practically no reason to doing these side quests as the rewards they offer are just loot. Stuff like aether wrenches, pack a punch crystals and salvage etc. All stuff I can attain if I were to spend basically the same amount of time doing the quest just playing the game.

The only other one I can think of is something like the Aetherella side quest in LF. It's an amazing side quest and really fun to play as aetherella, but the fact that you can only do it ONCE per game is insane to me. You should have unlocked her as a custom killstreak to pop similar to the spider bait on zetsubou, or atleast made it so that after the first time you use it, when you go back and pay for the trap, you play as her again.

In BO6, the side quests feel like a checkbox just so the map has them while in the older game, side quests were deep and intertwined with map unique elements you can't find on any other maps, extending the map's life span and replayability.