The current system is clearly broken ... for MLB coaches other then fielding, there is way more supply of coaches than demand ... so you wait until the end and get the best of the rest on the cheap .. or you get lazy and grab the best AAA coach for the MLB minimum and add to the oversupply next season
fielding coach is stupid for another reason, but at least there is some strategy there ... either you try to get a loyalty guy to ride on the cheap for a few years, throw crazy money at the half dozen capable coaches, or punt the role
there is no risk/reward for all but fielding, and too much risk/reward for fielding
I don't think they know how to "fix" the current system, so might as well dumb it down to budgeting by role