I don't entirely disagree that gRPC tooling is nicer and more complete in some areas, but there's some misconceptions here.

You can specify openapi v2/3 as YAML and get comments that way. However, the idea is that you add descriptions to the properties, models, etc. It's almost self-documenting in v3, and looks about the same in v2, although I've used v2 less so can't be sure.

I can't speak to editor support, but openapi has an online editor that has linting and error checking. Not sure if that's available as a plugin somewhere, but it's a likely a little more awkward if it is by virtue of being a YAML or JSON file rather that a bespoke file extension.

I've seen v3 share at least models across multiple files - it can definitely be done. String formats for dates and uuids are available, but likely not as rich as the protobuf ecosystem as you mention.

And I wholeheartedly agree that the lack of consistent implementation is a problem in openapi. I tried to use v3 for Rust recently and gave up due to it's many rough edges for my use case. It's a shame - the client generation would have been a nice feature to get for free.