"The idea is that skill training is really specific, so if you want to get better at a skill you have to practice that skill....exactly.”
Not very exactly.... A quote from Science of Sports Training:
The amount of resistance in sport-specific exercises has to ensure duplication of intermuscular and intramuscular coordination. If resistance is too great, the movement may resemble the external form of the technique, but it will require different coordination than the one that is best in the technique. For example, the intermuscular and intramuscular coordination in throwing a 1.5 kg (3.3 lb.) ball using the technique of a javelin throw without a prerun is the same as in throwing a 0.8 kg (1.75 lb.) javelin. In throwing a 4 kg (8.8 lb.) ball in the same fashion, the external form resembles the javelin throw, but the muscular coordination registered by an EMG (Electromyograph) is different. The throw with a 1.5 kg ball can be used as a sport-specific strength exercise, but the throw of a heavier ball—up to 4 kg depending on athletic level—may be used only as a directed strength exercise by javelin throwers below the stage of maximal realization of their potential (Wazny 1992b). In high jumping, vests with weights amounting to no more than 5% of the body weight are used in training forms of competitive exercises (Matveyev [Matveev] 1981). If the time, rhythm, or spatial form of a technique changes with a given amount of resistance, then the resistance is too great.
Here is Tom at 50: