Many undererstimate or misunderstand what a Great Coach is and does. Vince Lombardi was a great Coaching Coach. But he inherited a decade of First Round draft picks and merely organized them to produce until they all got old.
He then exited Stage Left and let Phil Bengston begin the burden of rebuilding. Ditto for the Steelers Coach, Joe Gibbs. Shula was a great cosching Coach but he couldn't rebuild the Phish into a SB club after the players George Wilson and the unbalanced Draft gave Miami, got old.
Walsh built the 49ers and retired to be a GM,when their player acquisition was much easier since FA had arrived, but the CAP had not. He is a great GM.
Only Paul Brown and Bil Belichick were complete Football Program Coaches/GMs. They built the Administration, the College and Pro Scouting programs, selected both the players and Coaches and won, multiple times.
In the colleges there were/are complete Football Program Coach/GMs. Bear Bryant, Jimmy Johnson, and Bill's friend and possible successor, Nick Saban.