From the perspective of someone who doesn't play Brand, I feel that, in his current state, he doesn't really offer anything to the team that another champ could do better. While his stun is really strong, it's too conditional to really consider him on a team comp considering a lot of other champions give much more reliable CC than him, the most prominent being Veigar's Event Horizon, which provides a stun that is both more reliable and eventually is longer than Brand's stun. And the sad thing is that Brand's stun is the only thing that gives him any sort of niche.
In addition, the RNG of his ultimate makes him too unreliable to use, especially considering its effect on an ablaze target should really be a base effect on the ability itself. It's an embarrassment of an ultimate, especially considering other mages have ultimates that will either straight up kill a target (Syndra, Veigar), or have massive AoE ultimates that can completely turn the tide of a teamfight through tons of damage, usually with crowd control as well (ie. over 50% of all mage ults). That's not to say that Brand's ultimate is weak, but it does have stiff competition from nearly every mage ult in the game, and its RNG makes it all that much worse.
That's not to say Brand is particularly bad. That's just to say that there's no real reason to play him over any other mage in the game.
