Sadly I believe you are right. There are people on the fringes of a "conspiracy" that are still open to reason. They want an explanation for their world gone un-understandable (as I like to calll it) for them. Their worldviews just broke and their sense of security and normalcy received a huge blow.
When the first soft lockdown was in place in Germany I stumbled into a small anti-mask/anti-corona discussion. There was a leader type (a medical doctor who should know better) that was unreachable. And there were some clear disciples of his. But there was also one guy who presented numbers and stats printed on paper about how much more deaths the flu season 17/18 caused.
Gladly I knew my numbers and could point him to some facts about the numbers. First he only had data about said year. That some few years before there were only two-digit flu death numbers in Germany he didn't know (and I could point him to the same source of original data he was quoting showing this).
The more and more I took his arguments seriously and only was arguing in a fact based manner based on his sources, the more I saw that he started to think about what he said. I also was clearly not putting him down and even stating, that some of the government's measures seem illogical to me (as they were at the time and still are), but that I - from the values I was raised with - valued the knowledge, that I do everything not to endanger people who cannot protect themselves as good as I can (they were mostly arguing against masks).
I argued that I am guided above all by the value of humanity and that I therefore follow the principle of caution and prefer to wear the masks in a store where I might accidentally get too close to other people, even if I find it unpleasant, rather than taking the risk of possibly endangering someone in the risk group.
While we talked, more and more people of this group as well as bystanders started to listen and I saw that at least in some parts the seemingly homogeneous group split into disciples and people starting to think.
Do I think I was able to argue somebody out of believing? Clearly not - but I am hopeful, that I was able to plant a seed. One would need more time and more real talks to really pull someone away from the fringes of a conspiracy. Someone captured deep within is imho sadly lost.
[Edit:]
Forgot - I really like your irrationality approach. Will copy it and try it.