Motorcyclists say the same thing about speed being a benefit and maybe it is in some cases, but if you look at the stats, the faster the bike, the more likely you will die. Speeding is a factor in 32% of fatalities.
I'd be surprised if it's significantly different on an e-bike.
In that range, and in mixed traffic (which is unfortunately most urban riding in the US), a 5mph difference can be a step change in terms of whether drivers even feel the need to pass me at all. 15mph is only 50% faster than 10mph, but can totally flip the "who's passing who" dynamic from "cars passing me frequently+aggressively" to "cars hesitate, back off, and then I get ahead / pass the next cars in line at the next light."
Here's an account where I've been posting videos that illustrate this a little more viscerally: https://twitter.com/CarsDontFitJC/status/1457490588320817153
I would assume the same about motorcycles and ebikes, but presumably the threshold would be lower due to lack of protection (motorcycle helmet and armour not as safe as a metal shell with airbags).
So I wonder where that curve starts to rise up on bicycles and ebikes considering they wear just a bicycle helmet and no armoured clothing usually.
(I loved riding ebikes in China (Kunshan) with wide protected lanes that were totally separate from traffic outside of city center (where speeds were low and congestion high, negating they need)).
There’s a pretty big difference between going 10 and going 20 too. Physics lets us know that 2x the speed of a mass carries 4x the energy, so a 20mph crash does 4x the damage of a 10mph crash. I’ve had a bike crash into rocks at under 20mph that could have killed me were it not for a helmet and padding. (I did not walk away unscathed, years later I can still feel the injury to my shoulder…)
Crashing at 60 on a motorcycle is pretty likely to kill you. Crashing going 20 on a bike might break bones - as long as you hit something stationary, rather than throw yourself in front of a car doing 40. Crashing at 10 mph and you might be able to jump off or walk away with only scratches.
It’s also fun to think about how crashing at 1000 mph is not that much more likely to kill you than crashing at 60 mph on a motorcycle. At some point, the speed is enough to do all of the damage.