I remember when I used a C program with CGI. It was quite fast, and this was decades ago. There were no >100 cores or threads, and RAM was not abundant either, it was at best 1 GB. It was doable then, pretty sure it is even more doable today.
Amazon in 1995 was a C++ executable invoked via CGI () That couldn't scale once load-balancing was required, but it worked pretty well up until that point.
() technically, two of them: one handled the front (customer visible) end, one handled the back-office side.
