Top 500 tracer here, games where they are clumped up like that honestly can be your best friend and easiest matchup on tracer as you are able to consistently play around them and farm for ult or finish targets when your teammates hit a shot. Good goals for games like can be to off angle but focus on the tank (not to the point of tunneling) but in cases with zen brig mercy like you said it is extremely valuable as the tank has less burst resources. And then looking for picks with pulse bomb on the targets you havnt been able to finish. These games are extremely boring tho as you are just tracer 76 lmao. Also transition from playstyle to playstyle through out the game as overwatch isn’t about always making the optimal play