I think the 9/11 and JFK conspiracy theories are dissimilar, almost opposite.
The official explanation for 9/11 is also the simplest possible explanation: terrorists carried out a very low tech and plausible hijacking attack that exploited some rather obvious holes in our airline security.
The 9/11 conspiracy theories are orders of magnitude more complex than this official narrative.
I don't think the JFK "second gunman" theory is more complex than the official truth. In it's simplest form (Oswald worked with another gunman, but there was no overarching conspiracy involving Russia or Martians or lizardmen or whatever pulling the strings) I would argue it's simpler than the official narrative.
While it is possible Oswald worked with another gunman, there is no reason for him to do that. Everything done is something anyone with basic gun knowledge could have done alone.
As I said elsewhere, the only evidence of a second gunman is we know Oswald was a good shot with a gun and so needing 3 shots (with a scoped rifle at close range - less than 100 meters) is something to question. But in the end it seems more likely he would have pulled the trigger himself and thus not needed help.
The official explanation for 9/11 is also the simplest possible explanation: terrorists carried out a very low tech and plausible hijacking attack that exploited some rather obvious holes in our airline security.
The 9/11 conspiracy theories are orders of magnitude more complex than this official narrative.
I don't think the JFK "second gunman" theory is more complex than the official truth. In it's simplest form (Oswald worked with another gunman, but there was no overarching conspiracy involving Russia or Martians or lizardmen or whatever pulling the strings) I would argue it's simpler than the official narrative.