Very interesting questions regarding the soccer vs. violin style of practice and myelination needs. In my own work, I've dealt with all possible points along that spectrum, so I'll provide some of the insights I've gained.
He also discusses how the soccer guy will have a huge network of possible movements that are well mylinated while the violinist will have fewer possibilities but they will be highly refined because being a world class violinist requires extreme precision.
Yes, and in order to understand what our needs are, we must first determine what our primary training objectives are, which is why I'm always on about that so much as being vital right from the very beginning of training. There is no such thing as "the" needs of the IMA practitioner. In this sense, his needs are no different than any other stylist's. It all depends on what he is training his martial art to be able to do.
Now in IMA we have a need for precision with certain maneuvers and a gargantuan network of possible movements to react to practically infinite variations and circumstances. So it would make sense to have both practice aimed at refining techniques to a high level of precision and practice that maximizes the time spent using those techniques.
Why, yes indeed. And you have just demonstrated an elegant use of reason to jump right to the answer. I have for many years advocated a 'many pieces to the total training pie' approach, and this is exactly why. It's also one of the key reasons why the whole 'ten years before learning to fight' model is not only unnecessary, it doesn't even make sense in terms of the neurophysiological reality involved.
Let's take a look at it. For simplicity's sake, let's call the work we do in that first ten years the "precision" work. Let's call the work done to develop actual combat skills the "combat" work. The precision work requires the kind of refined and extremely targeted practice that the violinists use. Toeing in from the gua instead of the knee in koubu, or pouring the weight distribution from one leg to the other instead of stepping it there. Adjusting muscular tension to arrive at 'sung'. Using the deep spinal muscles to generate spinal whip instead of the abs and erectors. These kinds of things.
In contrast, the combat work requires the kind of non-linear, random access broad networks of associations and related movement patterns that the futsol players use. The parameters for what constitutes "proper" movement is ever-changing, with a huge volume of relevant stimuli/information incoming on a continuous real-time basis. The myelination, and just as importantly, the associated engrams for each type of practice are very different. In fact, they do not exist along the same spectrum of training development at all, but are indeed separate skill sets entirely.
As a result, there is absolutely no need and therefore no reason for their respective development to occur sequentially the way they would in the 10-yrs before fighting model. Not only can they occur simultaneously without any disruptive or inhibiting influence on the other, they can actually produce a synesthetic and mutually beneficial development through what used to be called "dual encoding" in the field but is now more accurately referred to as multilinear access neuroassociations. IOW, in some cases, the development in one area generalizes into the pool of motor development patterns and becomes accessible to other skill sets, e.g., the balance you gained from ballet lessons helps you on the basketball court. Closer to home, the whole-body synchrony developed in jibengong or practicing the form can generalize to your combat responses.
When sparring slow you can also focus on your technique and pay attention to detail. How you actually are doing something and find the reasons it doesn't work. The real detail training happens with solo work though.
Ah yes, to some extent, but not entirely. Not all precision work is solo technique. Certain kinds of detail work are a function of the interaction of one's movement, structure, timing, pressure level, balance, force vectors, etc. with the opponent's/partner's. Solo practice simply cannot provide these factors for evaluation or modification. As such, it can be vitally important that that particular kind of detail work be corrected, improved and refined while still in the context of interaction with him. This is where practices like rou shou, tui shou, isolated drills and various levels of sparring come in. Further, the insights and improvements gained with a partner can often inform your solo practice in ways not otherwise possible by any other means.
All that technique training though won't help a bit if you don't try to use it while sparring, whether you go fast or slow. If you do your forms one way and your sparring a completely different way, then you are wasting your time. Your time would be better spend solo practicing the same way you spar.
All of this is why I like to use my analogy of building a racing car in your garage. You build a basic frame/chassis, then go take it for a spin to see if the foundational stuff is sound. Then you take it back to the shop and add some features, then back to the track for a test spin. Rinse and repeat and you'll quickly end up with a car that zips and also holds together mechanically in the tight turns.