I kind of dislike presence of meta terminology in fiction, even that based on video games. It's often immersion-breaking, and hardly has any real significance that couldn't be better described through other literary devices, especially those numbers and power scaling terms aren't put in context. Even when they do have context, the reader of a work of fiction will hardly appreciate that raw stats of a story based on a game nearly as much as they'd appreciate vivid imagery that illustrates what happened without referring to stats. >"His power level... It-It's OVER 9000!"
-doesn't always have the same dramatic effect.
I noticed that asian (japanese, chinese, korean) lite novels tend to do this a lot, especially crap mmo Isekais type ones. Instead of saying how high his charisma stat actually is, you should express his low charisma through his habits and mannerisms. Same goes for strong characters, as you should describe them physically or have them do feats of strength in both casual and dramatic circumstances.
Of course, creating a character with low charisma in reference to typical fallout characters might be appreciated by fallout players, but even if they have low charisma you should consider the impact on their behavior on the audience's perception of them if you want the readers to like the character. If you make them randomly edgy/dickish with little context, what could have been an endearing flaw could instead make your audience dislike a generic edgelord character.
A good way of expressing character's with low charisma would be to add some dramatic irony to the situation, usually by giving the reader direct insight into what the character is trying to communicate, through narration or internal monologue, and juxtaposing it with some graphic dialogue of the character spilling spagetti and failing to get the point across, preferably with some imagery of the character's tone of voice and visual's of either party's confused/offended expression, perhaps followed by some internal monologue or subtle narration of the low-Cha party mentally kicking themselves as they screw up. It has the opportunity to be comedic, relatable and cute, and decent for character development as characters are best developed through vivid description of their habits and mannerisms.
I've noticed teen novels like the Percy Jackson series tend to do this. Not saying those books are the best, but they do a decent job of illustrating autistic, ADD teenagers, which are an example of characters that I would consider "low charisma".
Pic unrelated, but I felt like posting anyway.