A solid pre-season can set an athlete apart from their competition and keep a team poised to dominate the upcoming season, however this does not complete the high-performance puzzle as the season progresses.
There is still room within a season to continue to progress your athletic profile to stay sharp and mitigate injury, which in turn improves overall performance which is the overarching goal of any training undertaken by an athlete or team.
As a preface, increasing your total training load as a season begins is not appropriate, so the ability to maintain athletic progression initially forms within appropriate progressive loading over a period.