there's plusses and minuses to both, obviously. a lot depends on where you are in your physical development. if you haven't had your growth spurt/been through puberty yet, there's less benefit you'll gain from working out all summer. if you've already gone through puberty or are going through it, the gains can be staggering. my 2023 son focused on gaining strength and flexibility during the pandemic and his improvements have been crazy. he throws the ball harder (t81->t87 from the mound), hits the ball harder (t83->t91 tee exit velo) and runs faster (7.6->7.1) in the 10 months from april to january. how much of that is natural growth and how much is due to the increased strength, i dont know, but he's a lot stronger.