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-...