I have worked on non-trivial (aka took 10-12 people over a year to even deliver an alpha) greenfield projects, where I literally made the first check-in into the repo.

The only 500+ line PRs I raised was auto generated boilerplate code, or renaming something.

I don't understand the optimism of devs who spend weeks writing code without bothering to test anything they've written. Unless you're writing utterly trivial BS, how does one have this level of confidence in their code? And if you did bother to stop and test, why on god's green earth would you not raise a PR? Why wait till you have thousands of lines of code before asking for feedback?