Lit 2 to Lit 3 was really minimal: https://lit.dev/docs/releases/upgrade/

As I recall inside Google it was maybe one in a thousand elements that needed any changes at all. I updated the entire internal codebase of many tens of thousands of elements in a couple weeks of part time work.

But more importantly Lit 2 and Lit 3 are interoperable, so there's not the same pressure to update. When an element or library updates from Lit 2 to Lit 3, it can do that as a point release, because its public API is the same. This really reduces the amount of upgrade toil you have to deal with.