You’re spinning in circles.
There are certainly people on the no fly, or “watch list” as you call it who are eventually allowed to buy guns. I don’t have a problem using the no fly list as a check for gun ownership. The biggest issue with it is if you’re incorrectly added to that list, it’s almost impossible to get your named removed....which is why Ted Kennedy and John Lewis kept running into issues. If then-active politicians can’t get their name removed, imagine how you would do so if you had that same issue?
Then you mentioned “terror watch lists”.
I think if the FBI has questioned you for a potential terror threat, if you try to legally try to buy a gun it should come under increased scrutiny.
My point, again, is I find it odd that a fair number of shooters have legally purchased guns after being questioned by the FBI, and don’t seem to have had any issue in doing so. It’s happened enough that it’s curious how it repeats itself.
Maybe you don’t find that odd. Or maybe you just like arguing.