Not sure I agree with you. Time is the factor.
It takes time at the table just to maintain your current level.
Additional time to learn new knowledge, additional time to practice that new knowledge, additional time before it gets converted to improvement.
Solidifying my fundamentals and mechanics made my game jump. I am still getting better, just at a slower rate. I am in the cycle I described above. Maintain, learn, practice, improve. Repeat.
I suspect given the amount of time I can devote to pool, I will peak out about 1-2 yrs. from now and then it will be almost all maintenance and very little improvement.
Correct, I should have clarified that my stance is dependent on time and health. In a perfect world if you have the time to devote to regular deliberate practice and competition you should continue to improve steadily, but not necessarily quick enough to reach the top tier (that's an entirely different discussion).
For many people, it's just not possible to devote the time and that is fair. But I think it is still possible to improve with limited table time, albeit at a much slower rate.