But I do like the fact that there is some differentiation of approaches even for characters who use the same skills.
... yeah, uh. The mechanics are, ultimately, an abstraction to give the game some structure and allow adjudication of success beyond "I kill you!", "nuh uh!", "uh huh!". If your end result and simplified method - "Persuade X to do Y", "I make a speech that convinces him" - are the same, the differences come from the exact content of your method, which is where the
roleplaying part of a roleplaying game comes in. Now, you
can sometimes call for different dice rolls. If my goal is "get into the compound", I could do it by hopping over the back wall or by disguising myself as a servant and walking through the gate in broad daylight. Those would be different pools, as the end goal is the same but the methods are different.
But the thing about Charisma and Manipulation is that they're really
not very different. The simple methods are mostly the same; "talk to people and make them want to do what you want". Much like Strength and Dexterity, you don't tend to
get charismatic people who don't know how to play off people's intimacies and so on - that's what makes them charismatic, whether it's conscious or not. Heck, ask half a dozen people what exactly the difference between the two is. Most will say something like "well Charisma is being truthful and a forceful personality, and Manipulation is being sneaky and lying a lot", and that's a
stunt difference, not something that should be coded into the mechanics. It makes no sense for someone charismatic enough to raise armies with their speeches to be completely unable to use that force of personality to lie to someone's face and project
honesty and
trustworthiness so well that they're believed... and yet because of the Cha/Man split and the fact that there's no point buying two "persuade people to do things" skills when you can manage perfectly well with one, most of them
are.
Differentiation of approach is the whole point of roleplay. If you're at the point where characters with the same stats are one-true-pathed and you
can't differentiate their approaches like that because Charisma 5 Manipulation 1 dictates that they can't lie at all or persuade people in any of
these ways using force of personality because those are Manipulation actions, you are at the point of 1e Lunars where they recommend you give your Full Moons different weapons so that you can tell them apart.