Ironically, the topic of the thread could be the SG that Rondo needs
I'd argue that he is the opposite of the SG that Rondo needs.
Rondo needs a SG who is a good three-point shooter to compensate for Rondo's deficiency in that area. Brooks is not a good three-point shooter.
Rondo needs a SG who can move without the ball. Brooks is considered to be bad at playing without the ball. If you compared Brooks to Joe Johnson on the Nets last season, Brooks had a higher usage % and had a lower percentage of his shot assisted.
Rondo could use a SG whose defense will allow him to conserve energy by taking an occasional play off. The words "matador defense" have sometimes been used to describe MarShon Brooks.
Brooks really wouldn't be a good compliment SG to Rondo because he tends to have the ball in his hands, which isn't going to work well with Rondo.
He isn't a spot up shooter. He is more of a slasher, who needs to be handling the ball to create (like a smaller/quicker Tyreke Evans, not a pure PG, not a shooter, but a scorer who functions best with the ball).
I think he is a better compliment for Bradley at PG (if we have to continue to suffer through that experiment this year). Bradley's defense compliments Brooks' scoring punch. Bradley isn't the best floor general in a set offense so he can hand the ball off to Brooks on the offensive side of the floor and make cuts away from the ball, which I think is his best role offensively.
Ideally you'd want a shooter who can hit threes on kick outs, but Brooks generally is going to need the ball in his hands to create.
That being said though, maybe experimenting with him in a role where he doesn't get to be the ball dominant player will help flesh him out more as a better overall player. Some of his main drawbacks are his turnovers and shot selection since the ball seems glued to his hands at times. If he is forced to play off the ball more he might become a more diverse scorer.