Original link: How Morgan Stanley Tackled One of Coding’s Toughest Problems / WSJ.
I think they are smart guys.
Ask the AI to do it all - translate millions of lines of code from Cobol to Java/whatever would likely not end up with a working system and even if it did the technical debt from day would be astronomical.
Ask AI to produce requirements from the Cobol code, do normal architecture and design by software engineers and then (not mentioned in article but I am sure they do as everybody does) use AI assistants to help with implementing may actually work.