It’s still possible to beat security. Someone who is dedicated enough to do it will find a way. I’ve always said that eventually they will find a way to take down or over a plane using only the items already on the aircraft.
I agree with your first premise. They will find a way to take a plane down.
I disagree with your second premise...with a single caveat...they become hired pilots or falsify IDs to act like a pilot.
Hijackers who openly proclaim their intentions will never control the plane for long.