I don't pay a lot of attention to coach hiring so it's not that big of a deal to me, but... I do think there should be an average coach for every franchise with an average level of growth. For example, can anybody off the top of their head tell me which ML team has a below average Fielding Instructor? These are the changes I would make under the current system.
1. Coaches can only be signed at the level they are listed i.e no signing Lo A coaches for Hi A positions and includes the addition of a FI at each level.
2. Coaches always resign with their franchise but every 2 years demand a promotion (unless ML). Coaches can not be promoted until they have completed 2 years at a level.
3. At least one average coach available for each position at each level and no bad coaches. I think it is trying too hard to make an artificial market and adds nothing to the game to have teams bid on average coaches and the absence of bad coaches would also keep an owner from destroying (especially intentionally) a minor league system.
4. Less higher rated coaches i.e. Pitching coaches with 90 + pitching IQ. This is where the bidding wars should take place. ( Think about the bidding wars on a 90 Lo A pitching or fielding coach.) There should be very few above average coaches, maybe 2 per level, but their impact should be significant. In lieu of Low draft picks turning into stars this is how low 1st round and 2nd/3rd/4th round draft picks should become ML players and stars. An above average coach should be able to add a significant amount of extra points to players.