I am not sure what you mean here I don’t see picking a guitar string with a pick any more complicated than performing a proper clean and press. Or heck even varying the fingers in different positions, but maybe we aren’t seeing things the same, and the words aren’t lining up cause they are just words. But I don’t mean they are the same thing weightlifting an music, I just mean the concept to start doing random things to get a different muscle striation hit to grow the muscle better.
By this I mean say I am trying to get faster at this USX stuff well gypsy sorta uses this concept so if I go and learn some of the phrases over here, maybe if I come back I might develop my picking with the USX electric realm a bit better. Switching it up. But yes interleaving these phrases with each other helps between the gypsy jazz realm and the electric usx phrasing helps, this can definitely help technique. I see it everyday.
Furthermore no amount of interleaving is going to get you faster like how he did it through microadjusting the speed. He listened, audiated, and played at the same tempo whether if it was .005 percent faster, he was still building it up in microadjustments whether he realized it or not in the moment. Otherwise he would be as fast if not faster than some of the really faster players. And maybe you are partly right, maybe it takes interleaving as well as microspeed adjustments to actually build up the bodies ability to go at that speed naturally.
So whoever the relative was we owe him a great deal of respect for him helping Lars Lannerback get better secretively. I mean they probably knew what they were doing helping him get better. You can change speed in DAWs in microadjustments. So the question remains was there a way to microadjust speeds with older recording equipment or was it really just a fluke.