How to fix Gibraltar

Gibraltar simply suffers from bad design. He is built to be a durable character, but he is big, has the same health as everybody else, has no additional mobility, and his passive only works when his aiming down iron sights, which is too slow to be used in a close range gunfight, and makes him stand out like a sore thumb at sniper ranges. His dome prevents both himself and the teammates inside from attacking through it, so it impedes both teams. That is not a net benefit. Worse, the best tactic with the dome is run-and-gun tactics where you pop in and out of the dome, and due to his large hitbox and low mobility, he is the worst at that.

His saving grace is the fact that popping his ultimate and throwing down a dome allows him to perform emergency revives like nobody else, but the extremely long charge time of his ultimate limits this. The best buff I can think of for him would be just making his ultimate charge much, MUCH faster. It synergizes with his dome in a way that his passive just doesn't.

EDIT: Buffing his passive so his shield activates instantly when he aims down iron sights, rather than with a 1 second delay, would also help.