Depends what you are trying to showcase I guess.
Your situation is a little different than most guys as you are getting pro interest already. I would always favor working out over playing organized summer ball for most young players. Guys just don't develop ability (work on pitches, develop velocity, get in great shape ect) playing 60 games over the summer. If you are a PO this hold true even more so as you are usually sitting around for hours a day in the summer heat waiting to pitch. At least this has been my sons experience. If you are playing in a that league will benefit draft spot or getting a great offer from a great school you want to go to maybe do that. Outside of that, I always favor training hard in the offseason. My son played mens league while working out and trying to recover from a back injury getting cut from his college team the year before. The benefit to mens league is he could work on things vs live hitters (although not great hitters) without having to worry about results or worry about getting pulled after an inning. So, he could treat them like weekly extended pens....starting about 60 pitches and working his way up to 120 pitches.
If you are going to do the workout approach, have a well thought out plan and make it your religion this offseason.
As for the article, it was a good read. There are those "late bloomer" guys. He had played in several years and was throwing harder than when he last played....he naturally finished growing and got heavier and stronger in the process. Not the norm of course. The article says most MLBers are throwing mid to high 90's....this isn't true. The MLB average FB velocity was 92 mph last year. Most guys out of the pen probably are throwing mid 9's now and velo keeps rising, but, that is an overstatement. 98 is still very rare.