Time invested isn't linear with improved talent. We all have our own thresholds, but we all get diminishing returns after working/practicing so many hours in a day.

It also depends on the quality of time as well as the quantity. I'm a musician, and it's a fairly common trope to talk about practice in terms of efficiency, such as identifying "directed practice" and similar terms. I've experienced it myself: if I'm mindlessly playing the same passage over and over again, I won't improve nearly as quickly as if I stop and analyze why I'm making the mistake rather than just trying to force myself past it.