As a Chamber main, I actually support a nerf.

I do agree both his headhunter should be raised (125 at max though, 150 would make them a little too expensive.), Ult Orb should be increased as your said, OR, they put a timer on it and you have to use your 5 shots within x amount of time (I would say 45 second to a minute, since most chamber mains pop the ult at the beginning of a round), BUT they also need to touch the TP. I would say increase the cooldown by 5-10 seconds. It is his most OP ability, and the reason he is so popular.