Are you sure it's better spent elsewhere?
You can't apply the "one size fits all" to this. If I have 4-5 young prospects are premium defensive positions, I need that expensive FI. If most of my prospects are pitchers or LF/RF/1B, not so much. If I have a ton of cap space, a set team and low IFA budget, putting money into coaching is a good place to put it.
There just is no right/wrong answer. That said, if you're putting 8m into a league average coach, you screwed up somewhere.