If you spend more time closing issues than creating them manually from discussions, the math adds up.
As a maintainers, if you want to be be able to tell real issues from non-issue discussions, you still gave to read them (triage). That's what's taking time.
I don't see how transforming a discussion into an issue is less effort than the other way around. Both are a click.
Github's issues and discussions seem the same feature to me (almost identical UI with different naming).
The only potential benefit I can see is that discussions have a top-level upvote count.
imo almost all issues are real, including "non-issue" - i think you mean non-bug - "discussions." for example it is meaningful that discussions show a potential documentation feature, and products like "a terminal" are complete when their features are authored and also fully documented or discoverable (so intuitive as to not require documentation).
99% of the audience of github projects are other developers, not non-programmer end users. it is almost always wrong to think of issues as not real, every open source maintainer who gets hung up on wanting a category of issues narrower than the ones needed to make their product succeed winds up delegating their product development to a team of professionals and loses control (for an example that I know well: ComfyUI).