Personally I found hitting with the “sweet spot” of a bat much easier to do and find than trying to find the sweet spot in a training regime.
Hope this is not too negative but there are so/too many variables IMO.
To me the real question should be trying to find that sweet spot (even if you only use the single parameter of how many days between a given type of session say) while said athlete still has time left in what should be the prime of their careers.
Take a college “career”, if it last 4 or 5 years, assuming one has a new coach when one starts (from whomever had that role in HS to the one who is either head coach or event coach in college) say 6 months to acclimatize to dramatic change in personal situation. And then how long getting to the stage where full value is gained from the training routine?
An athlete may only have a year or two left. My thought has always been get to conference/divisional in year one, use year two to step up to national level championships, and then spend the next 2 or 3 trying to get to the podium there.
Just the fact that we are all aging can play havoc with what seems to work one year, one season does not appear to be as effective the next time around. Yes, this is the “art” but at some point A LOT of time is spent just looking, so sooner or later does it not just become, at some level, just “going with what you got”?
Another major factor is trying to individualize this, even if in a small group to a coach training situation. I have found many coaches have trouble bringing training to a sufficiently individualized level to really succeed at finding a “sweet spot”. A head coach wants the best from the team, yet it should be individuals, each with their own “sweet spot”, making up that team. A problem I have always had in the team sports.
All we are trying to do is be more precise with decisions. That’s it.