> Those aren't exploitable XSS, but it doesn't hurt to have a second layer of defense.
The other suggests breaking clients that aren't using the more secure version of an OAuth method because
> I can't think of any OAuth client that would like to [use it]
That second one is a good idea, but the maintainer is also right to ask for some discussion before introducing a breaking change.
But crucially: neither of these are the kind of significant security issues you've found. Maybe lead with an actual bug?