It’s like everything else mate, practice makes perfect. If they constantly train on fitness and very little technical training with the ball, then yes they won’t be as good, but if they are constantly training and practicing with the ball, and at pace then they will rediscover that muscle memory to control it better. I remember a critique of the Martinez years was that a lot of the training was with the ball and so general fitness suffered which showed in games.
Was interesting to read a headline on a website today, where Gakpo and Salah confirmed that all they do is practice certain shots from outside the box and Gakpo scored from one yesterday. Beckham used to be stay behind and have a the hanging from under the cross bar, and would try and get the ball through the tyre. George Graham used to tie string around the waists of his back four so they would be aligned. There are little techniques in training which can allow players to perform better.
The history of football is littered with footballing anecdotes about players practising certain skills in training - I would be highly surprised if that level of detail formed any part of the training, with us (whether with Dyche or even before him)