I agree the problems you're describing are real and important to select for, but just requiring agile experience won't help you there. Lots of people practice a weird form of agile development, where they go through all the motions of fast iteration, but almost all tasks consist of non-negotiable internal dependencies and not value delivered to a customer.

I'd argue a similar thing is true for tech stacks. If there's some correlation between knowledge of all the fiddly bits of C++ and ability to write clean, performant systems-level code, I've yet to see it.