Yes... and most electric assist bikes cap out at 20 mph in the US, as required by law.
Also... you sound like you've never ridden a road bike seriously. 20mph in a bike lane, especially while going downhill, is pretty meagre for a standard road bike. No assist needed.
Hell, I'm fat (ish) and I can hit 25 on flat ground on my road bike with some effort (although staying there is draining). I can easily do 30 going downhill.
I'm regularly passed by folks doing more than 30 on hills where I live.
I forgot about that, downhill without pedaling brings most bikes a good clip, mine being no exception. I have a really good bike with great disk breaks I keep in good shape so I'm no more or less in danger than any other bike on the road. The biggest concern any cyclists have are crowded streets and poorly thought out bike lanes, not ebikes.
Also... you sound like you've never ridden a road bike seriously. 20mph in a bike lane, especially while going downhill, is pretty meagre for a standard road bike. No assist needed.
Hell, I'm fat (ish) and I can hit 25 on flat ground on my road bike with some effort (although staying there is draining). I can easily do 30 going downhill.
I'm regularly passed by folks doing more than 30 on hills where I live.