You haven't seen any plastic daytime soaps, I gather
On the topic of reallife.
Charisma is necessary for the projection of beauty, in the first place. At the same time, there are many ways to be beautiful, and many ways to be Charismatic.
Some people have high Charisma, but exhibit less talent at acting. For example, I consider Madonna an extraordinarily charismatic artist − with stage presence. At the same time for some people, this presence conveys less well via a movie. Nevertheless, she is arguably "very attractive" compared to "average". It is her Charisma that makes this attractiveness − her visual appeal − effective.
No but seriously, it's a fantasy game. The argument "it isn't realistic" is kind of watered down when you consider elfs and dragons, wouldn't you think?
Elves = supernatural beauty, persuasion, and magical Charm
Dragons = conflation of primal dangers, intimidation, and magical Fear
Still, make of it what you wish. I certainly am not arguing an Appearance score serves all tables.
I understand part of where you are coming from. You are saying, the Comeliness score is like a "numeric portrait" sotospeak. In the same way that player picks an image to represent the character, the player also picks a number to represent a degree of attractiveness.
But then, what seems like a contradiction, the DM will use this number to determine the outcomes of certain encounters, social or otherwise. So there is nothing neutral about this number. It is an actual mechanic in play, and invites the same kinds of meh that the 1e Comeliness score invited.
Ultimately, if the concept of Comeliness is in play at all, it needs to be well thought out, implemented well, and work well within the goals of the 5e game engine.
tl;dr: if you like it, use it. Otherwise, don't. Problem solved
With regard to quantifying the effect of attractiveness, its value might be something like: add half the Comeliness bonus to a Persuasion check, when in sight within 30 feet. So a Comeliness 20 is +5, divided by two adds +2 (or +3) to a Persuasion check, in addition to Charisma.
In other words, it is alot like Advantage to a Persuasion check.
In other words, a separate variable.
That its possible a high value in one increases the probability of a high value in the other can certainly be true.
Comeliness isnt a separate variable, because within the game engine it doesnt do anything separate. It isnt a game variable at all.
However, D&D doesn't track such interdependencies. For instance, I'd be hard pressed to imagine a Str 18 Con 3 person. But D&D doesn't make it any less likely than any other pairing (Str 18 Int 3 maybe?)
Here I agree. In the 5e engine, the player and the DM must pick the single most pertinent factor in a d20 Test, and ignore all others.
Adding attractiveness as a separate variable in addition to other variables, is something the Cortex Prime game engine manages better.
But we don't have any complex rules for connecting Strength to Constitution. And we certainly don't need any for Comeliness and Charisma
Strength and Constitution have discrete game mechanical functions.
Charisma and Comeliness have overlapping mechanical functions.
If anything, it is Charisma that matters, and Comeliness may or may not enhance it.
In other words, beauty is more like a tool proficiency.
Ultimately, the Comeliness feat works best, along with the Hideousness feat. Spending a feat represents an extraordinary, even magical beauty or fright.
The opposite of Charisma is unnoticeable and ineffectual − no presence.
Charisma includes the intimidating aspects of inspiring fear and repulsion.