You can either roll randomly and hope for high Charisma, or you can't play those things under the D&D ruleset. Not if they want to be taken seriously, at least.
That's a little . . . odd. Those characters seem solid, realistic, and well-grounded in the world. Personally I'd probably take them a lot more seriously than a character basing their entire fighting prowess on a squirrel-shooter.
The rules tell us that those characters are not viable upon the battlefield, and are likely to die.
Where?
I can see where it could be inferred from the rules that these characters are less-optimal in single combat on the battlefield than a fully minmaxed character. (And more optimal in avoiding combat in the first place probably.)
But what I don't see is anything to support your claim that they aren't viable.
The battlefields of D&D aren't populated solely by people with an 18+ in Str or Dex.
Having more friends willing to come along and fight alongside you is generally a greater advantage than being a little more graceful or athletic than your opposition. Outnumbering your enemy is almost always a 'viable' strategy.
A plucky stable hand is not a professional warrior, which is the reality that the fighter class is intended to represent, and it is disingenuous to model them as such. You're describing an NPC commoner or, at best, a rogue.
Professional warriors do not spring fully-formed from the brows of their parents. They generally have to start off as pretty amateur, apprentice fighters first and work their way up to veterans.
I am running a game where the social pillar is of such incredible value that the fighter dare not interfere, because failure is likely to get the entire party killed. You may have missed that part. This is a very long thread.
What does the Fighter player, (and presumably all the other players who aren't playing the party face) do when the party are engaging in social activities?
What happens when the party face just plain rolls low once in a while?
Sorry, but your example from the book does not jive with the description of the class that's in the book. A barmaid wielding a frying pan is simply not a "similar figure" to a veteran soldier or dedicated knight. Where did she get her formal training?
From a veteran soldier. (i.e relatively high level fighter) giving her personal training IIRC.
Yes, she started as an apprentice with little formal training (1st level) but training and experience made her into a full-fledged (level 3+ fighter.)