It has more to do with the years going OFF of the ledger than what has been added by Sitake/Helton.
Evidenced by USC having 34 wins in the 4 year period from 2016 through 2019 and BYU having only 27.
So you can't really say it's due to Sitake so much as you can say it's that John McKay's 4 consecutive Rose Bowls (and 3 top-5 seasons) from 1966-1969 were a lot better than Tommy Hudspeth going 22-18 over that same time period at BYU.