The DOT standard isn't good, but the US doesn't disallow helmets that meet other standards. You can buy Bell and Alpinestars MIPS helmets in the US today, no gray market needed: https://www.revzilla.com/mips-motorcycle-helmets

You're on a tangent of a tangent, but:

Old school helmets use the philosophy that in a crash, you want your head to be harder than its opponent.

New school helmet use the philosophy that a helmet should absorb or deflect as much energy as possible, so that energy doesn't get translated to your brain.

They are actually diametrically opposed. Fortnine (the same channel I linked earlier) has a video on the SNELL standard. Its origins are as a beefier version of the DOT standard. They recently found themselves at a crossroads where it's impossible to both meet SNELL and meet ECE 22.06 (today's state-of-the-art standard). They ended up bifurcating SNELL into two standards: one that meets old DOT-based SNELL, and another that basically says "if it's 22.06, they can call it SNELL variant B." It was the only way they could keep the SNELL brand alive across both halves of the transition.