It’s according to what you mean by “play nice”. If you mean never criticize, give in to whatever the subordinates want, etc., I agree. But it’s hard to believe that a highly successful HC has employed that approach.
OTOH, if “be nice” means treating subordinates with respect, encouraging them and seeking their best interests within their responsibilities, yet always holding them accountable, always following through instead of cursing them or degrading them or showing them “who is boss“, then I disagree. I’ve been on both sides as a subordinate and superior and I know this approach works and with most it works much better.
OTOH, could be a difference between most Southern kids and most Western/non-Southern.I know Saban recruited a bunch of kids who are not self-motivated (i.e., needed someone to drive them) especially early in his time at Alabama. Maybe too many are of those types are still in the program.