To me, what it comes down to is that role players should not make the rest of the team have to change their game. Its not that Evans is a poor offensive player who rebounds. That would be fine.
But Reggie is all over the place on both ends. For all he disrupts the opponent, he also disrupts the Sixers. On defense he's randomly trapping PG and taking random fouls and lane violations. On offense he keeps setting up shop in the low post and occupying the lane, and yet the play is over if he touches the ball.
All of this chaos can be a net positive if you are playing a superior opponent, but on most nights he is just putting too much pressure on his teammates to cover for him given that he is just a role player.
Theo, on the other hand, has similar linitations on offense, but plays a very conventional game. he does not demand the ball or take crazy risks on defense. He brings his positives and tries to hide his weaknesses. That makes him a great role player and doesn't hurt his teammates when he is out there.