The scenario you’re describing is true of just about any vehicle where the occupants are not restrained. The airbags do not actually absorb much of the energy from a collision; their main purpose is to hold the occupant in place. Crumple zones help by reducing the acceleration from a collision, but if the occupants are not wearing seatbelts then the vehicle will be a deathtrap regardless of size or safety features.
There are two ways to reduce the effects of an impact. Spread the applied force out over time, and spread the force out over area. You also try and prevent vital areas from direct impact so those areas get effected less.
Restraints spread out the force over a greater area, as well as distribute that force to areas of the body that are better built to handle that impact.
It's better to take that force across your waist and chest which are much better designed to handle it than having you head smash into the windshield or the thinner steering wheel that gives less smash into your ribs.
An airbag spreads out the force over an even greater area. It also cushions the impact to some extent, by spreading out the force over time. They reduce the acceleration of the person, rather than the acceleration of the whole vehicle like crumple zones do. They also try to apply force to even out the force on your body so your torso doesn't get decelerated faster than your head which can can be very bad for your neck.
Crumple zones help by reducing the acceleration from a collision, but if the occupants are not wearing seatbelts then the vehicle will be a deathtrap regardless of size or safety features.
True. Because the passengers are much more likely to take a localized impact on the dash or window rather than have that force spread out more.
However crumple zones reduce the overall acceleration felt by the passenger compartment. A more massive vehicle also reduces the overall acceleration in a collision between two cars because more of the impact will be felt by the other vehicle that way.
What a rigid passenger compartment tries to do is prevent intrusion into the passenger compartment by objects that might produce force in a localized area damaging it more.
A lighter vehicle is more dangerous than a heavier one.
A vehicle without crumple zones is more dangerous than one with them.
A vehicle without restraints and airbags is more dangerous than on with them.
Both big cars and tiny ones can have airbags and restraints.
The tiny one can't have crumple zones, and regardless of the design of the frame usually has a harder time preventing objects from intruding into the passenger compartment, and the larger vehicle can always have a better protected passenger compartment.
The more massive vehicle will always take a lower portion of the impact force.
We can talk about unrestrained occupants, but once again they are still safer in the larger vehicle, because they will get tossed around less.
The smaller vehicle always has the disadvantage, they are just trying to lessen that disadvantage with a rigid passenger compartment.