I think in traffic you are fairly vulnerable to both, but on a bike, at least if you fall, you don’t have the insult of your own vehicle crushing you as well as whatever obstacle / other vehicle you hit.
On the other hand, many motorcycles come with sacrifical rubber ‘sliders’ where if a motorcycle is dropped to the ground, the only thing that touches the ground is still the wheels and the rubber sliders on the dropped side. The slider itself is a block of rubber and it’s $10 to replace when ground down sufficiently to a nub.
I’ve found weight to be a less of a problem than I expected in practice.
The bicycle leaves me exposed in traffic and more often than not wearing a t-shirt for heat control.
Just to give a different perspective on it.
The bit I found most terrifying on a motorbike is seeing a car pull up to a stop , about to turn onto the road I’m on (with priority) and wondering if he’ll stop.
On a push bike, I’m doing maybe 30-35 kph in a city, and can stop very quickly. Splatting into the side of a car at this speed (less some braking) is serious but unlikely to be very dangerous.
On a motorbike, suddenly I have 200kg gyrating under my pelvis about to crash, and bounce into the traffic. Just feels terrifying.
And crucially, this situation (not the crash but the scenario) happens all the time.
https://www.motorbikeclaims.org.uk/blog/these-shocking-accid...
(And still 17X more than in an automobile.)