Perhaps you forgot the word ADAPT, also the part about sparring/training with different people, bigger, stronger, faster, smaller, slower, weaker. With the first 3, learn to adapt, learn to use your skill against difficult opponents, the 2nd 3, play, experiment, adapt, learn to conserve energy, try new things, a different approach/angle, things to you can then test against the more difficult opponents.
Imo, I agree in part, for example, there are some arts, that teach x amount of grades in technique, and x amount of routine movement, which becomes predeictable, very little or no sparring, or a tippy tappy point scoring competition once in a blue moon, and always train with the same person, here you have a very valid point. We used to call that one dimensional, they had a lot of skill in a confined area, no nuance as you put it, a difference or graduation of difference, like a piece of music, I have heard this thrase many times over the years, nuance, the problem is, like music, nuance needs to work off a beat,mor rythme if you like. Stopping the learning process, no longer adapting, thinking you have the magic formula, this is the problem, your nuances are different to mine, mine are different to JP's, its just you beleive yours is better. There are things to be learnt from Mma, and its data from matches and performance based training, but its just another nuance, adapt and use whats useful, then move on. Nuance.