He also has a 5-6% BB% for his career and is in an era where he will increasingly see more and more off speed stuff. I think expecting a huge breakout, beyond the 2.5 WAR type that he has been, is not as likely as I would have thought a year ago.
They could have sold at the 2017 deadline (JD and Happ would have had 1.5 years of control left, and Stroman/Osuna 3.5 years each). Regardless, they didn't need to tear down. They could have traded JD in mid 2017 and still tried to win in 2018. Maybe they use that saved money in free agency, or to acquire a player in trade, etc. Not being able to leverage the assets they had while still being able to fake an attempt at contending is definitely on them. Rogers wants to make money, so of course they won't want to rebuild when attendance is high, but that should not have prevented Shatkins from trading certain players in order to maximize the return.
What percentage do you give any of those players turning into 2-3 WAR types, especially in this organization? 10%? 5%? It's pretty damn small. At least with Grichuk you can hope on a 3+ WAR path if he puts things together, but the others are huge long shots. As far as development, almost nothing in baseball is linear, but there are indicators to show breakout potential. For me, BB% is huge. If you're a 5% BB type, then I'm not counting on that player turning into much unless he has a Javy Baez type of hitting ability, and that's not very common. Base running is important. Defence (which Shatkins typically ignores) is important. Exit velocity and stat cast performance is important. You can't just look at age and some minor league numbers without context and assume a player has potential to improve.