“Ultralight” and “bomber” are at odds with each other. For bulletproof rain protection, I like Outdry (or a silnylon Packa/Poncho). Outdry is more like “light” than “ultralight”, but it cannot wet out, so it is less likely to encourage condensation under the jacket.
AFAIK, EE Visp is the lightest 3L jacket with pit zips. It is pretty great for an ultralight jacket. I would be careful about bushwhacking in it. Like most WPBs, it wets out after half an hour of heavy rain, so expect some condensation while active. The light weight makes it slightly less warm than other WPBs, which is an advantage in warmer weather.
Rab Phantom is often called the “lightest”, but it is an anorak so I would not even consider it, personally. Oddly, I have never seen anyone comment on the Rab Cinder Phantom, which is an actual jacket made of the same stuff (7D Pertex Shield 2.5 layer). Rab claims it is 100g (3oz) in size Medium, which is as light as WPBs get. Wear long sleeves under it (at least a Brynje), because 2.5 layer does not protect the membrane from the oils in your sweat. Same caveats as Visp regarding condensation.
For bushwhacking I would try military surplus, like the ECWCS L6. Users like them, and they are reasonably lightweight for tough garments. I have an L4 — it isn’t exceptional for weight or breathability, but it would be my first choice for bushwhacking.
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