That's true. If you equate it to, say, lifting weights, you see that extremes under either approach can result in fatigue and injury.
Consider those who hit a body part once per week vs. those who hit every body part 3 times per week.
The once per week guys annihilate whatever muscle group they're hitting that day...and hope that the week rest gives sufficient time for recovery/healing. Go too heavy or too many sets and it sometimes catches up with them...sometimes additional rest/time off is prescribed.
The 3x per week for each body part guys generally do less sets per body part and less weight...knowing they'll tax that body part again in 2 days. Go a little too many sets or too heavy and there's a good chance of fatigue and injury.
The key is to (1) identify what approach works best for this lifter..or in the case of baseball players, each player and (2) manage not only the players game-time load, but pre and post performance conditioning. In the case of lifter, those who stick to the approach that keeps them fresh and healthy perform better over the long-run...some simply can't stick to the plan (push too much weight, don't rest enough) and hurt themselves.
Since pitchers are managed by their manager/pitching coach, they alone don't make the decisions of what situation to be in, how much rest to get etc. right?
Where I'm going with this is that I think GENERALLY teams try and identify where a player is best suited...body wise...to perform with the least chance for injury and other complications. Unfortunately, even once that is identified, SOMETIMES I think a team considers what is best for the TEAM, despite the data and observations they might have regarding that pitcher's best interests.