I would assume there is a point at which if you just do base training (i.e. Mostly slow mileage while adding in tempos, cruise intervals, ancillary work etc.) you will stop getting significantly faster to the point where you essentially aren't improving at all. We are also assuming you have a bona fide method of knowing when an athlete has reached "max base fitness".
Say you take an athlete like Rupp who ran 13:37 in high school, you choose a guy like him because he is already fast enough to be close to elite/pro level and he's young enough to where he can drop a ton of time. What you do is you have him run the base phase until he is "maxed out" and then have him run hard intervals and peak him for 2-3 all out Time trial efforts per "season" to try and break records (eventually). Then once the record attempts/races are over, have a rest period and then start back up with the insane base training. Wash, rinse and repeat.
This is a hypothetical and just a thought I had, I don't really think this would work out all that well but I'd like to hear thoughts.