Running improvement isn't actually like this, except for beginners.

First, you actually do quite a bit of periodization at the season level, so you might have a long base block, followed by a more stamina/quality oriented block, then race specific sharpening, followed by taper and an A race, and then rest. Improvement is distinctly non-linear across these phases, and you'll actually start each season fairly far behind where you were at your peak.

There are also plateau effects, where you've basically adapted as much as you can to an existing stimulus and you need to find new ways of triggering adaptation.