There’s a lot of misunderstanding around this stuff. Technically all you need for a bomb is the ability to go prompt critical on demand which you can do at surprisingly low enrichment levels. What’s a useful weapons grade enrichment to you has a lot to do with your delivery systems not some universal constant. If you’re looking to fit something in a WWII bomber or early generation ICBM that imposes specific limitations.
And yes, in an alternative universe where delivery systems also just appear out of nowhere, you could sprinkle a million tons of 1% uranium over a city.
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.