But that begs the question, it doesn't answer it.
The issue here isn't, "Was Pitt's recruiting good enough between 2013 and 2017?", because most would probably say no it wasn't relative to the level most want to achieve. So the fact that recruiting didn't change much is indicative of a lack of 4 star recruits.
This would probably be the reason why it's like that for many other teams as well. Most teams don't recruit good enough to compete for much of anything. This is why the same few teams are dominating college football every year.
I would agree that within teams that don't have top heavy recruiting classes, the average star ranking doesn't change much. When you remove the filler on the backend, you just have more filler on the front end. But when you look at teams capable of getting a decent amount of front end, impact recruits, small classes often do impact the class average. Another example is USC in like 2012 or 2013 when they had one of the highest average star rankings ever for a recruiting class, but it's because they only took like 10 players.
Because those front end recruits account for a larger % of the class average compared to a normal year. If that isn't the case, it's because: 1. You're currently Ohio State or Alabama and there is no filler anywhere in your class, or 2. You aren't getting enough 4 star commits for class size to impact class average. It's all 3 stars across the boards, so whether you take 15 or 25, the average doesn't change.
The latter case is the issue that many are worried about. Current recruiting is nothing but middle of the road 3 stars. So the class average isn't impacted by the class size, because how could it be?