I respectfully disagree. Once you know the core, say 25%, which I've seen devs with 5 years experience in unrelated language pick up basics in a couple of month

I respectfully disagree. Once you know the core, say 25%, which I've seen devs with 5 years experience in unrelated language pick up basics in a couple of months of full time practice, and then become pretty good at after a year, then switching between teams that use different parts of the remaining 75% is as painless as anything else. I've seen people struggle way more with differences in web development dev envs than c++ and JavaScript is supposed to be simple! (It is but all the rest of the complexity of work comes along for the ride too no matter the language.) Of course c++ isn't the right tool for every job and as each decade passed there are more languages that do certain tasks better.