Regarding resting the arm for pitchers. With some research you could find out how the best pitchers in baseball went about this on their way to the top.
I tend to agree with the rest theory, but I haven't found any real proof as to what is best. All kinds of approaches have proven to fail and have proven to succeed.
Most Latin pitchers throw year around with very little rest as amateurs. There are and have been a lot of great Latin pitchers.
Checking our files on Zach Greinke while he was a junior and senior in HS... He not only pitched, but played in almost every game at 3B or SS. He pitched in the spring (HS), Summer (Travel Ball), Fall (Jupiter) and Winter (PG World Showcase) both of his last two years in HS. He even caught at the last World Showcase he attended. At that event, he popped a 1.85 at 83 mph velocity. Threw 90 across the infield and threw 94 from the mound, all in the middle of the winter. Then he pitched in HS, was drafted in the first round, and signed for something like $2.5 million in Marietta Georgia while playing in a summer WWBA tournament. A couple years later he was in the Big Leagues. This year at age 25 he enjoyed his best season and I hope he wins the Cy Young Award.
I only bring this up because it (Pitching/playing year around) didn't seem to slow him down. All people are different, maybe Greinke wouldn't have been as good as he is had he taken the mandatory rest period. Don't know, we only know how things turned out the way he went about it.
I would say that things turned out pretty well.