The certificate and rules sound mostly good. A private pilot's license isn't a commercial license, it's fairly easy to get, but ensures that you know the 'rules of the air' like a person with a driver's license presumably knows the rules of the road.
The rules of the air are useless 400' above the earth - they're only designed to allow pilots to operate around other aircraft, and these drones won't operate there, at least not for now. Frankly, if they ever do operate autonomously at altitude the rules of the air that exist today will be worthless anyway.
A pilot's license is also not easy to get. For starters, you generally need to not be terrified of flying in a small plane, which by itself is something probably half the US population would fail to satisfy. Mostly it is about stick and rudder skills that are useless in a drone, and which also not everybody has. It is also very expensive - at a minimum you need about 40 hours of flight time, much of it accompanied by an instructor. Planes rent for about $120/hr in most places, if you want something from the 70s.
while self-driving cars are allowed on the road for testing, unless they're on a closed track they still need a rated human driver available to take over if something goes wrong, etc...
These drones aren't being allowed "on the road" - they're being restricted to below 400' and in fairly uninhabited areas. You're legally allowed to operate a fully-autonomous vehicle in your back yard without any human inside as long as it doesn't go out onto the roads. Otherwise you'd need a license to buy a Roomba.
If Amazon wanted to test landing a drone at KSFO then certainly requiring an instrument-rated pilot at the helm would make a lot more sense - they're going to be in controlled airspace talking to ATC and essentially operating under IFR in an environment where a mistake might kill hundreds of people. This isn't that.