Sure, talent matters. Stars are a little to subjective after the 5star and high level 4 stars though.
Other than the elite kids who can play, contribute, and excel right away (who I would argue in some cases are simply farther along in physical development). I would say the difference between, say a 4.1 and a 3.3, after a year of college development, when all else is equal (attitude, effort, etc, etc) is pretty close if not the same. Same goes for the mid 3 star and high 2 star.
Unless you can stockpile "elite" talent, redshirting, development, minimizing attrition, and identifying diamonds will remain important.
Kids can have massive physical and mentality changes from 17-21, especially with college facilities and development programs...some kids way more than others.
Basically, in many but not all cases, I would bet a lot of the 5 and high 4's have simply developed quicker, and are closer to their peak.
By the time a low 3 star with upside and 5 star, at same position and similar variables, reach their junior/senior year, I'll bet the gap isn't much, if any...
Sure, getting more ready made talent helps...it helps depth, competition, etc.
One thing that doesnt get mentioned much though is the Position of the player, in respect to the Star ranking....oline, dline, lb, TE...Iowa's strengths most good years...positions that in my view can be "developed" moreso than RB, wr, cb, s, qb...where inherent speed, skill, instincts can be recruited but Iess so developed