This is an area I've constantly have had to fight for. I ask development teams to loop in SEO as early as possible to true understand the scope of a migration. It's not just let's migrate from point A to point B. Research, resourcing, and testing all have to occur. What's more, if issues occur and things go off the rails, there have to be contingencies. I'm really happy to have see a video specific to migrations!
It smells that Google as search engine era comes to the logical end - migration would take 1 year with 301 redirect ? Are you joking dear John Mueller from Switzerland? P.S. to developers: never use 301 redirect - Google dramatically drop your ranking, do 404 or even more 410