“if it was straight sarin, in shells or in a tank, then a conventional explosive could disperse it, even at low efficiency.”
This is true - but, one of the “good” things about nerve agent, is that it pretty much either kills you, or it doesn’t. Blister agent, or chlorine, can horribly scar, blind or disable victims who survive. If you suffer non-fatal poisoning with nerve agent, you pretty much just recover. To get the high fatality rate they had in Khan Sheikhoun (87), and have had in other areas, which were clearly targets of the regime, you would need efficient dispersal.
I would also point out that chemical agents in Syria are unavoidably a major intelligence priority of Israel - they simply must be. I think it a safe bet that Israel has deep understanding of what is going on in Syria, regarding chemical weapons - they did not just fall off the turnip truck.
The US is claiming one bomb was dropped in the street that dispersed Sarin. So far nothing has been provided despite the claims that officials could see chemicals dispersing from the bomb. Ive seen photos of that small crater in the street before it was cleaned and it looked like a rocket had fallen.
Good points btw. Would a single munition provide enough dispersal? Have you seen the photo of the street crater that the US is claiming is from the Syrian bomb? There was enough left from the Ghouta attack to tell exactly what type of munition was used and it was a ground launched rocket.