I think this is a rather out dated view. I'd argue the frontier models write better C/C++ code than many, many, many junior devs.
With that said, I agree with your larger assessment of needing to keep junior devs and teaching them things that are likely never written down and only kept in the mind of a gray beard.
The solution needs improved documentation and mentorship, not just hiring junior devs. And unfortunately I dont think the way things are heading companies are willing to invest. Why have a $150k+ overhead on a junior dev when $50k in token costs for a senior dev will take care of things?
But models past Opus 5.5 level abilities will make less errors than the normal above-average human coder.