By extension, this works both ways: when you train a single skill, and everything else is left behind, then you train progressively slower as that skill runs further and further ahead of the other. Likewise, if you train a low secondary skill, you train faster since the primaries are way ahead.
This has, to my knowledge, never been stated. The only thing that has been stated is the fact that secondary skills speed up if they are far behind. Do you have any facts to back up these comments, or is it an (educated?) guess?
What is high and what is low is a
relative concept. An inept skill can be high if everything else is atrocous. It will be 'less high' if everything else is awful.
That is, if you train, say, a low skill, it becomes progressively higher as compared to the other skills (even if it is still 'low' in a way) and as such its speed should slow down. Since it is difficult, if at all possible, to draw the line between what's high and what's low in
absolute terms, I imagine it works in reverse in the other end.
I haven't directly posed the question as you put it to a BB, but what I have inferred is as I stated it. Obviously I have no direct knowledge of the training process, so the best I can do is speculate.
I hope this makes some sense. I am getting lost in it myself.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."