While I generally agree with the "if it ain't broke" sentiment, you have to perform some pretty wild mental gymnastics to end up calling COBOL the "best tool for the job".

Adoption and ease of learning should always be considered when selecting a tech stack for a solution. COBOL's semantics are so foreign to modern programming languages that it makes the language pretty inaccessible.

Also, COBOL's strength is in the generation of reports, but in the end, it's no more expressive for that purpose than any general-purpose programming language coupled with a nice report generation library.