SUVs are mainly safer because they are bigger than other vehicles, although to a slight extent it also because they do better in crashes w/stationary objects.
if everyone just keeps buying heavier vehicles in an endless race to exploit other drivers, drivers will be less safe overall because collisions will occur with continually increasing force, not to mention the loss of maneuverability increasing crash frequency, while the marginal benefit of stationary object collision safety diminishes.
if we all drove smaller cars, we'd be a little less safe in stationary object collisions, but a lot safer in car to car crashes because crumple zones would have less energy to absorb. we'd be safer overall.
there is a cutoff with downsizing too because at some point you aren't safe enough with common obstacles people hit like deer or barriers and it outweighs your v2v benefits.
but the right direction currently for overall driver safety is still towards downsizing imo.
as a policymaker i'd push for smaller cars, as a consumer i'd push for bigger. luckily we have government to save us from tragedy of the commons