I really don't have an answer. But yeah if you're going to play a BP game, go to your best guys if the situation calls for it, even if it's in the 5th or 6th or 7th inning.
Ideally I wouldn't have pulled my starter given he was only at 81 pitches, has been dominant to this point and you were still winning 3-2. Kooch was working his way out of this and that BB wasn't a bad walk at all in that situation.