It must have depended on where you lived. My 1953 house had 2 prong NEMA 1-15 receptacles but there was a ground present. The Romex with the 16ga bare wire in it. I was just a kid who was learning about electricity when I pigtailed NEMA 5-15s everywhere and later when I got my first bug eye tester, they were all good.
Later in life IBM gave us ECOS testers that did test the grounding integrity under load and verified <1 ohm ground impedance. It also wanted something greater than 0 ohms to catch bootleg grounds.
The purpose of the ground is to create a very low voltage delta between the case of your appliance and the surrounding "earth" reference. That is only as good as the integrity of the grounding electrode and the grounding path in the branch circuit. It is also why NFPA finally decided in 1996 that we should not be using the neutral to ground things. There will be voltage drop in that neutral that shows up as a voltage rise at the appliance.
The major difference between AC and MC cable is the little bonding strip in the bundle that shunts out the wraps in the armor and prevents it from becoming a choke. That choke effect is also what limits FMC as a ground path to fairly short runs. I would still use a green wire ground tho, no matter how short the run is.
The relatively new "MC Lite" has a much larger bonding conductor inside and is OK for grounding and you are not required to connect that bonding conductor in the box.
I completely agree retrofitting just about anything but the normal 5-15 in a box can be challenging if they were sized to the normal "2x the largest conductor" deduction for the device. I am sure it has been proposed but I think the oversize devices should get a different fill specification. I ran into this trying to put USB receptacles in. One work around that doesn't look horrible is to use a surface raceway box over the regular box as a box extender.
When I was working for the state one of my inspections was to test the integrity of WWII era EMT installed in a building they wanted to use as a hospital. They wanted to be sure that old EMT was sufficient for the redundant ground path. I was surprised but every one I tested with my Ecos had less than 1 ohm of impedance. I was glad I wasn't the one snaking in the new green wire tho.
