Presumably anything popular enough has a good chunk of terrible devs?
I'm guessing there are some very unpopular languages out there that the % of highly skilled devs is pretty high, but I don't know if that means much ;)
Certainly. Depending on your definition of terrible. There are people who can keep the things running, but only do patch on patch to keep things together, but no architectural work, making more and more mess and we'll knowing they are unreplacable. (Partially encouraged by bad management direction)
Are there bad COBOL developers still practicing? FORTRAN?
What about Ada? Erlang? Smalltalk?
The mainframe families?