> that memory safe languages have fewer memory safety issues than languages

That's what I would assume ;-)

By the end of the day it's also a question of performance. For embedded, realtime or mobile core technologies there will always be a need to shortcut.

> Asking for hard proof is silly in software.

Not only in software. That's what the scientific method is for. That needs time. Currently there is a debate whether the switch from Ada to C++ for the F-35 is the cause of all the observed problems and budget overruns. There is still not enough data to know. But there was a decade-long track record for Ada in avionics. And C++ also had to establish itself for twenty years before anyone dared to develop an F-35 with it.