Without Alphonse you wouldn't have Marana, without Cirucci you wouldn't have Style, without Esmeralda you wouldn't have Medicine (she didn't train you in person, but it's through proximity with her and being under her medical care that you unlocked the skill). That seems pretty important to me? You also generally got more XP for sticking around Cirucci and getting involved in her quest for power than you would have for doing your own thing on your own. I didn't specifically lock that XP as "Cirucci is training you in this combat skill so you get XP automatically assigned to it" because I value player agency in deciding Nemo's build, but it's still more XP for training under someone important. On top of that, while it wasn't codified in mechanical traits, Nemo needed Alphonse to successfuly create Jackelton's uniform on a deadline.
I didn't mean to imply that unlocking the skills wasn't important. It's not what I was getting at.
In the narrative, Alphonse didn't just teach Nemo the barest basics of Maraña and leave her to work out the rest for herself; he's been teaching her and guiding her, so her skill in the craft has been improving faster than if she was trying to work it all out on her own without help. Mechanically, however, all he's done is unlocked the Maraña skill. If a hypothetical metaphorical bus fell on him immediately after he unlocked the skill, Nemo's improvement in Maraña wouldn't have been affected in the slightest.
In the narrative, training is supposed to unlock a skill, but also be an ongoing thing that allows a student to learn faster than if they tried advancing on their own. Mechanically, the only thing training does is unlock a skill. This is a mismatch between narrative and mechanics, which is what I was getting at.
Medicine highlights the mechanics-narrative mismatch. There is narrative reason to explain how Nemo unlocked the skill and is advancing it, that's not the problem. The problem is with how it contrasts with Style - another Mundane skill. Nemo has been learning Style under the keen tutelage of the foremost master of the skill, whereas her skill in Medicine comes purely from experimentation with no one to show her the way. Narratively speaking, Nemo's skill in Style should progress far faster than her skill in Medicine due to the presence of a teacher, but mechanically, there is no difference. Interaction with Esmeralda unlocked the skill and then when the metaphorical bus fell on her (her leaving Hueco Mundo), Nemo's rate of advancement in the skill didn't slow down at all despite the lack of a teacher.
Getting xp in taught skills would've been one way to bridge the gap between mechanics and narrative, but it's understandable why you didn't go with that. That said, it wasn't the only way to bridge the gap. Another way to bridge the gap while keeping player agency is to modify the xp requirements for skill levels like you did before, making them bigger or smaller to represent the presence of a teacher or lack thereof. It's a good simulation and it retains the players' ability to decide Nemo's build.
(One idea I've had is to remove the Unfavoured tag from Combat Arts to represent how if Nemo wanted to learn the skill, she would learn it at the feet of one of the best CA practitioners in Las Noches.)
Even if you don't go with the above idea, I do recommend thinking on a way to bridge the mechanics-narrative gap. This doesn't feel like it's an unfixable issue.
The reason I'm bringing this up now is because of what happened early in Chapter 10.
"She will teach me," the Bestia says. "That is my price. She will teach me Gran Rey Cero."
It's not fair, you think. I should be the one. The first to whom she should show her secret, the first to learn it from her.
Cirucci wants to learn Cero from Nemo, a Master in the skill. Under the current paradigm, there is no mechanical difference between her practicing Cero on her own and getting taught to Cero better by someone who knows how to do it. It won't just be Nemo who'll be the subject to narrative-mechanics mismatch.
As an addendum to all of the above, if there
are differences between growing a skill by getting taught and growing a skill by self-learning, then the problem is instead that they haven't been made apparent enough in the story/mechanics.