But no pilot should be content to attempt to takeoff with <90%. That's gut feeling at least; surely. nd it's 2 pilots who stopped thinking, not just one
Sometimes <90% is an appropriate N1 at lite weights on long runways. ( 16R in YSSY at 65T= 88%) I agree with your basic sentiment though that there would be some mental cross checks to enquirer as to why such a low N1 was produced by the EFB).
With low experience pilots poor management of workload ( rushing) often means that common sense cross checks are simply not done, the data is simply accepted. With more experienced crew rushing is also a problem but being dog tired is a more likely culprit for not trapping what is an easy error to make.