Let me ask a different question. Large refactor that ended up in a 60K line python PR because the new lead didn’t feel like merging it in until it was basically done. Even ask other devs to merge into his branch and then we would merge later.
How does one handle that with tact and not lose their minds?
Refuse to merge into their branch. If you have serious test coverage and the refactor doesn't change behaviour, it'll be fine.
If you don't have test coverage, or if the "refactor" is also changing behaviour, that project is probably dead. Make sure there's a copy of the codebase from before the new lead joined so there's a damage mitigation roll back option available.
How does one handle that with tact and not lose their minds?