To add some data -- below are the # of Top 5 recruits landed since 2015 (results may vary a little depending on choice of recruiting rankings):
8 - PSU, Ohio State
5 - Arizona State
4 - OKST
3 - Michigan, Minnesota
2 - Cornell, Iowa
1 - Iowa State, Lehigh, Missouri, Oklahoma, Penn, Stanford, Wisconsin
Top 10 in that period for Nebraska: Red. (Berger was also Top 10, but before 2015, so I can't easily find class rankings.)
Top 20 in that period for Nebraska: Breske, Labriola, Serrano, maybe Hardy?
So, yeah, I'm really not worried about Manning recruiting Shapiro or Mullen or anyone else Cael might consider a priority recruit. I'm sure he'll try, but there's no evidence to believe he'll succeed.