No worries
I think it's true to say there's reasonable and rational people backing Leave and that it isn't an insane idea of itself, but I think it's also a fairly decent argument at this point to say that they're either overly optimistic around what'll happen should we leave, or perhaps primarily motivated by concerns other than economic performance. Arron Banks for instance, one of the biggest donors to UKIP, said recently that the projected loss of £4.3k per person in GDP was "a price worth paying" (I'm not saying the figure is true there, by the way, just that he was willing to accept it as worthwhile). For some, the questions of sovereignty and border control will take precedence over monetary loss. Which is fine if you're a multimillionaire gimp, but not so much for a single parent struggling to get rent together every month. For others, issues surrounding immigration do hit them in the pocket, so they're making a rational decision based on that. But in general, the economic argument doesn't really ever seem to fall on the Leave side.
You could also turn your original proposition on its head and ask why the current PM and Chancellor, previously seen as heir apparent, would tie themselves to an institution that: diminishes sovereignty that they'd surely want back as head of government, prevents them from bringing the migration figures down to the levels they'd promised before coming to power, and stops us pursuing all these bilateral trade deals that would make as even better off upon leaving? They'd presumably have some pretty good reasoning for doing so. If there was a vote in the Commons, using your previously posted figures, Remain would win by a landslide, which also kind of puts a hole the argument surrounding a lack of democracy.