>>migration to their cloud mainframe offering was even more expensive for the raw compute
Mainframes were always cheaper. The only reason things like Hadoop and MR even picked up for heavy batch jobs, was because in the last decade lots of cheaper consumer hardware was available, due to companies having over invested in building data centers. The excess capacity was sent to hadoop work. If you have continuous ongoing investments in Mainframe tech or wish to start something new, you are better off using Mainframes.
Mainframes were always cheaper. The only reason things like Hadoop and MR even picked up for heavy batch jobs, was because in the last decade lots of cheaper consumer hardware was available, due to companies having over invested in building data centers. The excess capacity was sent to hadoop work. If you have continuous ongoing investments in Mainframe tech or wish to start something new, you are better off using Mainframes.