DD skipped fall ball and played other sports - volleyball and basketball up to 9th grade. That was her mental and physical recuperation time. Her summer team also had team practices in late fall and winter, either indoor or outdoor as weather permitted. Going into 9th grade she started weight training/core development in late fall. Sometime in December she started working again with her pitching coach to work on new pitches, and things she felt she was having problems with the past season. IMO, if pitchers don't stop and evaluate where they are skill-wise, they can't build a plan for improvement. That's not to say she didn't work on her skills at all in fall. She spent a LOT of time with physical conditioning and strength training - especially legs.
Honestly, she simply didn't have time for fall ball. When high school rolled around, it was wall to wall games from March through July without a break. Now, if you don't really work seriously on skill development, 5 months of games isn't much. But if you have intense workouts, team practices and other sports - you're going to have a full plate. Add in school work and maintaining grades to pile on more. And I didn't even mention swinging a bat...
Thinking back, I think our plan worked pretty well. DD accomplished her goal to be a DI college pitcher, got 5 years of college education pretty cheap, and is now using her teaching degree to earn a living for herself. Nope, wouldn't change a thing.
Our plan worked for us, but may not be ideal for another family. You just have to make a plan, adjust as you go along and keep a sharp focus on your goals.