I don't think longform gets so much visibility. Would be nice if clients intermixed normal notes with longform that could be expanded with a click, but I see the reasons why the community chose separate things.
Best bet is still to advertise your longform via kind1, but how to link is the problem. You can post a deep link to an existing reader app, but that breaks the flow of normal usage. You can use the nostr: protocol prefix, but support for that is few and far between, and just posting the event ID is still not supported everywhere. But maybe it's because of lack of author adoption.