> This design goal remains true up to this day, and only started to diverge relatively recently when C was updated to include features that were not supported (yet) by C++.

This is not really the case. See https://en.wikipedia.org/wiki/Compatibility_of_C_and_C%2B%2B for a non-exhaustive list.

It is true that both sides agree that compatibility is an important goal, but it's only a goal, not something that's 100% the case.