COBOL was the state of the art when it was designed, but any evolution on top of that is, by necessity, limited by a 60-year-old core design. While it _has_ produced a lot of real world value in the almost 6 decades of its existence, starting a new project in COBOL would be ill-advised.

Existing projects were written in whatever language for whatever reasons, it's "Would I start a project in this language today?" that's the bar to beat in terms of language "quality" and, in that sense, COBOL is a fairly low bar for most domains.