Hi! Brand main here. I gotta say from experience that as long as you have 20+ games as Brand and have a solid grasp on positioning and how to land your combo on a semi-frequent basis then he is very OP as support in lower elo.
That being said, once you hit around Plat 3 it becomes a little harder to dominate as Brand due to his lack of CC as support and lack of mobility as a damage dealer. Needless to say the better the players become the harder it is to land combos as often. He's still really strong, but only if your team has a good amount of CC either in the top lane or jungle, otherwise a good cc support will more than likely take control of the game; hence why you don't see Brand every other game in diamond+ elo.
It's still a huge b*tch to lane against though. He's quite the tilter :). <3