Does Brad rely too heavily on his stars? several injuries under his watch

[Moranis]

No.

This. Nothing else really needs to be said.

Also, if I remember correctly, Stevens has, in the past, been criticized for not playing his best players enough.

I mean it seems pretty obvious. Lebron James is in his 18th season (plus he has played enough post season games for over 3 full seasons) and hasn't missed a game and is playing 34.7 mpg (and is 5th in total minutes this year). 

Stars play.  You rely on stars.  That is how you win basketball games.