It’s not about delivery systems just appearing, the logistics of tossing around nuclear weapons in the Middle East using modern technology allows for a vastly larger bombs without significant issues.

You can buy a used A380 for a few 10’s of millions. Convert that to a drone is fairly cheap, and you end up with a deleverage system vastly cheaper than the cost of producing a nuclear bomb.

Obviously a subsonic aircraft isn’t ideal, but historic ICBM’s ended up being designed for multiple bombs that’s a lot of leeway if you use the same system to deliver a single bomb. What the US considered weapons grade in the 40’s through the Cold War is based on assumptions that simply don’t apply here.