After playing brand for awhile, here is my thoughts

1 - His ranges are way too short

Not only that, but different from LB ( a short range mage ) or Annie ( a heavy aoe CC mage ) , brand can't easily farm like them without using a lot of mana. He also has bad sinergy with mana regen items, has no mobility, and his CC is very situational and single target.

2 - His mana costs are way too punishing

For a champion that, to a maximum potential, should be combo'ing all the time, his mana costs are way too high ( lb is also a combo champion, but her burst is more safe, and she has a LOT of mobility ). I think he need lowers mana costs OR more rewards on hitting his abilities ( maybe a buff to W damage, more range spread on his E to minions, dk ).

3 - His ultimate needs to be prioritize champions more

I hate when I ult someone, and the ult hits them only once, and the rest it hits the minions.

4- His AP ratios are way too short.

His abilities are not even spammable. His Q has only 0.65 ap ratio, his W 0.6 and when the target is ablaze, 0.75, and his E has 0.55. Only his ult has a decent ap ratio IF it hits the same target 3 times