>No big rewrites or anything crazy
I think those are the key points why they've been welcomed.
And I would say especially for operating systems if it gets any adoption irregular contributions are pretty legit. E.g. when someone wants just one specific piece of hardware supported that no one else has or needs without being employed by the vendor.
Potential long time contributor is somebody who was already asking annoying questions in the irc channel for a few months and helped with other stuff before shooting off th e PR. If the PR is the first time you hear from a person -- that's pretty drive-by ish.
I always provided well-documented PRs with a narrow scope and an obvious purpose.
Not to mention LLMs can be annoying, too. Demand this, and you'll only be inviting bots to pester devs on IRC.
Drive-by folks tend to blindly fix the issue they care about, without regard to how/whether it fits into the overall project direction