This is 100% made up. I just replaced all our Enzyme tests with Jest tests about 3 months ago. The process is very straight forward. No way this would ever take 5 years. No matter how big the code base is. It is basically grep + replace.
Very surprised about this decision. I use strict languages much more with LLMs and they improve quality a lot. Working on a big python codebase is very painful with an LLM.