See where it says "Pro Years" 4.
That means he should be on the BL squad.
Players generally develop a great deal their first 3 seasons, and then after that they only sporadically gain points here and there. You can see that he HAS gained a few points this season already, so in my opinion, if you want to maximize that development you'd want him under the 89 Coach and not the 78 guy.
You"re only 7 games out of the 2nd WC spot, so if this guy would be the 2nd best pitcher on your BL staff, there's a really great chance he could be the difference maker. Unfortunate that it is already after the all star break, but you've still got 70+ games left, i think that's enough time. basically only need to gain one game every 10...