Nice guy, but nice guys don't win in the NBA. Too soft for this league and doesn't hold his guys accountable.
Spoeltra's a nice guy. Vogel is too.
I have some gripes with Brad, but this idea that he needs to be a raging lunatic at all times isn't one of them.
Sure, both of them are nice enough guys, but they also advocate for their players, demand respect from their guys, and hold them accountable, too. Both of them also work the refs when need be and chew their guys when they're not doing what they're supposed to.
Brad doesn't do those things. He doesn't hold any of his guys accountable, which is why they end up with these bad habits, and he simply doesn't work the refs - which is absolutely an effective and needed strategy of NBA coaches.
Smart is a perfect example. In 6+ years, Smart has essentially walked all over Brad - even chewing out his own coach on the bench on multiple occasions - and Brad has done nothing to address this or address his consistent poor shot selection at times. That's because Brad is just a soft coach and we all know that Smart is an alpha.
Beyond his obvious weaknesses in in-game management, his soft demeanor and character is absolutely another weak area of his that really limits his ability as coach.