I see your point, but I'm less worried about it it's potential to grow. I think most Qanon believers are generally older, and essentially less savvy on internet culture, so don't recognise the significance of the fact that this originated on 4chan, because they don't comprehend the trolling/larping/edgelord culture of 4chan. I think with an emphasis on explaining this calmly and patiently, most people will recognise they've been duped. And they won't have much influence on younger people, except some who are particularly vulnerable/susceptible.
I remember seeing a Twitter account do this a year or so ago. They set up an account claiming to be "JFK Jr", announcing a countdown to their return. They got 10s of thousands and followers, and on the date of their announced return, they posted a lengthy, detailed, calm, and sympathetic explanation of how the larp originated, about 4chan culture etc. The vast majority of responses were all accepting of this news and recognised they had been duped, despite having previously been eagerly anticipating JFK Jr from the dead to overthrow the US government.
I guess some people will refuse to accept they've been duped, but I just can't see the movement ever growing from here to anything like it's prominence during the last US election.