A 6.0 moves on court very differently to how a 3.0 would. Your fast 3.5-now-5.0 friend is unlikely to be moving the same way now than he did when he was a 3.5. If he is, then he either had amazing footwork for a 3.5, or his footwork is still terrible but he’s incredibly fast with very high endurance.
Stroke technique and footwork are somewhat tied, although quite loosely. Split step, crossover steps, footwork in general—I consider those as part of technique, ie skills. Perhaps not stroke technique if you want to be strict about it, but they usually come hand in hand. At lower levels there may be a notable discrepancy between the two, but the limit before your footwork skills bottleneck your performance is not particularly high, so IRL it’s rare to see someone whose stroke technique and footwork are at very different levels. Most of the time they are people who are coming from different sports, eg football (soccer to you), basketball, or badminton, but if they’re committed to the sport their stroke technique catches up quite quickly.
You’d be hard-pressed to find someone who can hit 6.0 shots (ie near perfect technique) with 3.0 footwork however. At best it’s someone whose technique looks nicer than it actually is, with terrible footwork (eg me). Even obese, former high level players retain their footwork—it’s their fitness that prevents them from moving as well as they should (eg carrying around 80 lbs more than they should), and even then they’d spend less energy covering the court than a 3.0 with 3.0 footwork who weighs the same would.
I actually played tennis a few times with a triathlete. He tires before I do even if I’m just hitting cross court to him so he doesn’t have to move much. Poor technique is poor because a lot of energy is wasted on movements that have no effect or influence on the ball that comes off the strings. No player who arms all his shots moves only his arm to the ball, even if he’s already in position and only needs to hit the ball, eg oserver or BSSH. Some part of the body is being overused (arm), other parts move around unnecessarily (360 spin), while parts that ought to be used sit around either doing nothing or nothing relevant (legs). Over say a three set match all that energy that goes into the unnecessary movement adds up. Good technique may not improve your actual endurance, but it does minimise energy wastage, not just in stroke production, but also by preventing you from having to use more energy than needed to cover the court. IMO TTW is guilty of treating stroke technique and footwork as two completely independent things, but they work too closely together to be learned in isolation. You don’t shadow swing a forehand 50 times in a row without split stepping each time you finish your swing, injury or old age notwithstanding.
