I generally don't have to worry about spotlight hogs, but this line of logic often leads to this idea that allowing the high charisma character to "shine" during social encounters is fine, because then the high strength low charisma characters will "shine" during combat.... but that is false. A bard with Expertise in Persuasion and access to Hypnotic Pattern is massively impactful in social encounters AND redefines combat encounters. Meanwhile Rune Knight can be impressive during combat, but has nothing to do during a social encounter.
I'm fine with social characters to be more free to act in social encounters, but alternatively, I want non-social characters to have a chance to do something other than say that they perform the help action.
I think we are both in agreement, just with different concerns and priorities. I've rarely if ever seen these "crafty" players you are so worried about, because generally the only time those low cha characters get involved is when they get swept up in the story, and I have seen that moment in their eyes when they realize "Oh god, I [bleeped] up, now I have to roll, and I can't reliably make this roll" which is a shame, because then they feel like getting swept up in the story was a mistake.
I would like 5e to have more overall balance among the classes, and have actually taken steps in that direction via home rules, but discussing that would be pretty off topic.
Interestingly, I don't even allow the standard Help action (boring auto-advantage) unless you are proficient in the skill being used (something the One D&D playtest is also doing). However I allow "non-standard" help when a creative idea is proposed, and generally lower the DC as a result.
I do not use crafty as an insult, I like crafty players. I just think that, as a DM, I need to be careful how I reward them, so other (possibly less crafty or simply less experienced) players don't get overshadowed.
The thing is though, then their action is meaningless. The bard with a 10 strength flexing for the thugs is more likely to intimidate them than the Goliath Barbarian with an 18 strength. Even as you lower the DC, the difference between a 1d20-1 and a 1d20+10 is 11 pts. You aren't generally going to reduce the DC by that much.
And, your choice of terms reflects a viewpoint. You keep talking about efficiency, about crafty players, phrasing the entire conversation in terms of this player who seems like they are trying to manipulate the DM and the game. I'm looking at this from the perspective of a player who has seen that scene in the movies a dozen times and thinks "Awesome! I can do that thing I thought of when I made my character!"
They are trying to recreate a moment from a book or a TV show, which was never a moment created to subvert some system. The system is just there from the game, and getting in the way of the story. Not always, but sometimes. They want the story beat, not efficiency.
I wouldn't expect a bard with 10 strength and +10 to intimidate (thanks to charisma and maybe expertise?) to try intimidation by muscle flexing. If they choose that route, I'd probably
increase the DC (unless they were intimidating an halfling child or something). I'd expect them to try intimidation by subtle coercion, with a DC decrease if they actually manage to uncover enough information about the target ("Isn't your family living in a farm just left of the city gates? What a nice, cozy home it is!").
And, well,
should the Goliath Barbarian with 8 cha and no intimidation prof be as good at the job than the bard with high Charisma, proficiency and maybe expertise? Heck no, imo. Lowering the DC allows the untrained low cha Barbarian to be adequate at the task, which I believe is more than fair, and ultimately kinda numerically the same as allowing him to use Strength...but:
- the calculation happens on the DM's side of the screen, as it should for reasons I explained here;
- if the barbarian player happened to invest a 12 in Cha instead of an 8, it gets a better bonus, which, I believe, is fair and logical.
Finally, I do not come from an adversarial DM mindset, if that is what you're suspecting. I am a mechanically minded player and DM. The story is important to me, but I've always believed that a good story isn't enough to fix unfun gameplay, while on the contrary, good mechanics will always improve one's enjoyment the story.
EDIT: I realized that I've been illustrating my position on Alternate Ability Scores for a while now, and spent a lot of virtual words doing so. Perhaps a change of topic would be best?