Amazon said its drones fly under 400 feet and weigh less than 55 pounds."
There are several issues with that, the first being that 55lbs from 400ft is a lot of mass traveling really fast...
But assuming they somehow make them perfectly reliable, you have the issue of other air traffic and obstacles that aren't on charts under 400ft.
Yes, yes, someone will quote the rules about altitude and airplanes. Someone forgot that helicopters exist, and that airplanes do sometimes fly lower as well.
A lot of light helicopters do not have any technology to avoid other traffic other than the Mk1 eyeball, and an Amazon drone may well not see one in time either.
It'll be interesting to see, but given many years of flying experience in helicopters, I shudder to think the first time a 55lb drone hits a helicopter. A big helicopter (think S-76) would probably survive it, a Robinson R22/44 would likely not.