It can definitely be true, but it depends what your service does, if you do regular HTML pages what you want is an infrastructure that can do fast string handling, for that I wouldn’t pick C++.

And if you need more developer time is also a consumption of energy.

I think a more common problem is relying on general frameworks regardless of platform. Frameworks solves a general problem, but you solve a specific problem, as your example shows.

How much would it save to use SQL SELECT with the columns you need instead of a ORM that fetches everything?

Or what about API endpoints that deliveries everything to single page app that only needs a few values?

Most data deliveries online today is never used only to be discarded. And you have that discarding of data at two different places, between the database & the backend and then between the backend and the client. That is probably a higher cost than changing server language.