It certainly was about a payday and it was also about being appreciated/wanted. In that sense, it was beneficial to Bronco, in addition to getting to move to a P5 team.
BYU needed a change. That stagnation of 8-5 year after year, beating only the teams he should beat and figuring out ways to lose to teams like 2015 Missouri and 2013 UVA. Being completely owned (it's more than 5 years of being owned) by your rival. This change was VERY beneficial to BYU.
If that isn't the definition of Mutual I don't know what is.