How far do you take it though? What if someone knows c+cgi? I forget the exact quote, but something along the lines of 30 years experience doesn't mean much if it's the same year 30 times.
Your quote is apt, but it cuts both ways. Using the same old tool indefinitely, even when newer tools can do the job better and much faster, might be foolish. On the other hand, learning to do the same task over and over again using different tools, each only a modest improvement on the last, might also be foolish.
In the case of your C+CGI example, I would agree that it makes sense to prefer any of the more modern "scripting" languages, which typically have both good library support for networking protocols and much more powerful integrated string handling than C.
On the other hand, there is little offered by any mainstream language ecosystem today that can't be achieved at least reasonably proficiently using tools from the .Net world as well (ignoring the obvious limitation of having to run on a .Net platform).
However, if you already know how to do something well in one particular stack, then you should just stick with that if the objective is to ship.
The operative word is of course that you know you can do it well in that stack. If you start thinking "there has to be a better way" then you should seriously look into alternative stacks or whether you are using your current one correctly.