This is a gold cage opportunity I've known a couple of people who worked as COBOL/mainframe developers in Europe at huge companies and their pay was definitely

This is a gold cage opportunity I've known a couple of people who worked as COBOL/mainframe developers in Europe at huge companies and their pay was definitely worse than what they could have gotten as a "a data engineer maintaining Spark" or anything else even similarly modern. The cage works both ways, on the one hand they might be hard to replace, but equally they'll have at least as hard a time finding a new job if they quit. Depending on where you live, the company you're working at might literally be the only company in that city using that particular tech stack.