If my home a/c is rated at 3 tons, using the same metrics what would be the same kind of rating for my late model 4Runner a/c? It's not well insulated, has a lot of glass area and the a/c works well no matter how hot is may be outside.
I believe a car's AC is the same order as for a house, in the 2+ ton range for the reasons your list. Cars aren't well insulated and have a lot of glass.
Plus, you expect your car to cool off from sitting in the sun in 100 degree weather in a few minutes.
Try get your house at 80F down a few degrees, takes quite a while.
A 3 ton ac unit has a 3 hp compressor, or slightly under. The rule of thumb is 1 ton = 1 hp, not sure about automotive, I would guess most cars have a 1/2 - 1 hp compressor. I realize the power loss is much higher than 1 hp when being used, I have read up to 10 hp lost with ac on in automotive. Not sure why, maybe inefficient form of power transfer to turn compressor.