I work in child car seat development and I can second that the main issue for our mechanical engineers is preventing neck injuries. Rearward-facing car seats really are a lot better on that front.
ADAC is indeed the main test, but even more difficult than getting a good ADAC score is passing the plus test[1], which focuses on neck spinal forces.
[1]: https://www.vti.se/en/services/laboratory-and-testing/crash-...
ah yes! I knew I was forgetting something - the NCPS techs we talked to gushed about the AxKid that they had finally gotten imported to the US
I wish the Plus test included detacheable rear-facing seats too. we dropped quite a pretty penny on the Cybex Cloud T because of how well it scored elsewhere