For the bigger vehicle, perhaps, but a smaller vehicle, even if up to modern standards, is less safe due to the larger one.

unfortunately it’s an arms race at this point and the only correct choice is to get a bigger vehicle to protect yourself

E=1/2mv^2

The energy of a crash at the same speed is linearly scaled with mass though. Especially when you have two such monsters collide, it's significant.

I expect energy dissipation scales in a similar way... e.g. I'd expect a head-on crash of two light cars to be roughly comparable in severity to occupants to a head-on crash of two heavy cars. Is my intuition off here?

For the same speed, the total energy would be Car-v^2 vs SUV-to-Car-v^2

But the smaller cars are probably more carefully designed for "crunch" zones, preserving their occupants by maximizing the effect of available material. The nominal energy involved vs Cars would simply scale as Mass of SUV in Cars.

Right, I'm aware of the energy the calculations give, but I don't see a good reason to assume that smaller cars have more efficiently designed crumple zones. I'd expect crumple zones on larger cars to scale in energy dissipation roughly linearly with mass. (Assuming similarly structured cars - e.g. I'd expect cars with safety cages and body on frame vehicles to perform differently from unibody vehicles.)