There’s that point, too, but once you have say 1.8 critical masses of sufficiently enriched uranium, how hard is it to make an artillery tube inside a bomb casing, put a .9 critical mass hemisphere at one end, and a .9 critical mass hemisphere at the other and put a big explosive charge behind one to drive it into the other?
Your argument only addresses Biden’s specious “they don’t have a weapon to put it in”. Mine calls that into doubt, and also points out the fallacy that we’d know before they did. If they’re building a copy of Little Boy, the test will be the attack.
Israel know it. Anyone who knows the history of the run-up to Hiroshima knows it. And anyone who claims we’d know before they had a weapon is either overconfident in our intelligence capabilities, clueless about nuclear weapon design, deluded, or selling something. (In Biden’s case, I’d be on all four.)
The same experts that said Pakistan didn’t have nukes right up to the minute one was exploded??