I know the biggest weakness of Brimstone is that his smokes are outclassed by the longer range, rechargable Omen smokes, but his stim obviously needs some work too.

What if the stim could be deployed but activated manually later on, and in addition to the functionality it has now, it could slow enemies down? That would create a synergy with his molly and ult and he could use the buff in reaction to being pushed onto more easily. I think the stim having 2 different uses would be an interesting way to create more diverse gameplay for him. But yes, his smokes need work too.