There's a story told in the book Atomic Habits where a photography class was divided into two separate groups. One group would be purely graded on the quantity of photos they produced, while the other would be graded on quality.
The professor was surprised to find that all the best photos came out of the quantity group. Over the course of the semester they were busy taking photos, editing, experimenting with lighting and refining their skills. Meanwhile the quality group was merely speculating and planning without much action.
This last week I watched the Steph Curry documentary: Underrated. Every level he played at, Steph was written off and second guessed because of his size. When he did succeed everyone was shocked. Here's this small, scrawny kid, how could he be so good at basketball? What they overlooked was the fact that he was spending all of his time playing basketball.
Like the quantity group in the photography class, he was busy experimenting with his shot and dribbling skills and finding his feel for the game. He was working on and getting repetitions of the actual thing (basketball). This level of foundation is the most important for long term development no matter the sport.
The whole world was telling him to work on something besides the game, his size. He worked on the actual thing (basketball). A habit must be established before it can be improved and far too many athletes are skipping past the habits of their sport. Development happens through repetition and there is no substitute, just do the actual thing and then do it again.