Yeah, that is often the case, but not always. And since it’s worked into the stats instead of called out as specific features, it just ends up looking like loose design instead of unique traits.
I will take the opposite side of the argument from you by saying that just naming something does not make it a "unique trait", if that trait is subsumed during gameplay. To me, that's merely performative design. A creature having "Keen Senses" written in their statblock does not make that creature more unique in their design when all that results from that is the DM rolling two dice for Perception checks instead of one. To the players... unless the DM specifically calls out that the creature is rolling with Advantage (and even then, most players I don't think care), the players have no idea that this monster has this so-called "unique trait"-- especially when the results of it being used are no different than any other creature who rolls Perception normally and just rolls high. So what's "unique" about it? None as far as I can see. All that's really different is in the statblock itself
when read by someone has one less line of trait feature, but that means nothing when it comes to actually playing the game. And that's why I call it performative design... it makes the reader think what they see is somehow special and necessary, but when actually used as its meant to be used it does practically nothing unique whatsoever.
To me, it's no different than when people would say that feats in 3E were "important" to differentiate their characters and that the game had to have them. Because a whole lot of these so-called 'important feats' would do nothing but just add a point to an already-existing stat. Which means that other than a person
reading the character sheet to see that the PC had this thing... in actual gameplay no one could ever tell the difference. A player could take the so-called 'Dodge' feat... and add a +1 to their AC. A feature no different than dozens of different ways a PC could raise their AC. So what did their PC being able to 'Dodge' actually mean at the table? Nothing whatsoever. When you see that PC being played at the table, are they 'Dodging'?... or are they just wearing a slightly better set of armor? Or is their Dexterity slightly better? Or is their armor magical? None of us would know. Because it's not like the player themselves would narrate their PC doing anything different when at attack missed them-- like choosing a specific attack roll number to say that
this one number was the specific one that the 'Dodge' feat they had was applying to and was the +1 AC bonus attributed to "dodging", and thus narrating on that specific roll each and every time that the character "rolled out of the way" of that attack just to justify having the 'Dodge' moniker attributed to their PC. Nope... that 'unique trait' of Dodge was just one in a series of numbers all add up together into a singular AC soup that the player never cared about except the final total. Their AC was 19. That was the only thing that was important. And all the small individual pieces to get to 19 were not important, the player did not care, and thus those pieces being "important" to the "uniqueness" of their character were actually nothing of the sort and merely performative in name only to the person who was reading the character sheet.
If Dodge was an actual different and unique game mechanic, or if something like Keen Senses gave you a completely new ability that was actually different than what one would already be doing... then yeah, I'd be more willing to say those things could be meaningful and their loss in 5E24 would be felt. But losing a feature that just duplicates or gives a slight bonus to something they can already do (and which can be completely negated as a bonus anyways by someone just rolling the original trait really well in the first place) is not actually losing anything of meaning.
Others will feel differently, and that's fine. But at least it it explains why these monster trait losses in 5E24 don't actually matter or affect me in any way.
