Those nations do not have the ability to defend civilian infrastructure - it's the weak point we see in Ukraine.

Nobody does.

These are large regions, AA coverage is narrow, using F16s to shoot down Shaheds wears down fast.

If Iran has stockpiles, and the wherewithal for mission planning, they can steer them around AA and hit the 'back office' at will.

Those states also have no practice coordinating the in-between methods - they have only very expensive ways to stop Shaheds, and only jet fighters outside of AA coverage.

Now - hitting a lot of things like civic buildings etc. doesn't have much effect, but it depends how the civilians react and cope.

Some very specific things like energy desalinization are acute problems.

These are authoritarian states that can keep information dispersal minimal and the civilians will just have to 'eat it' - but only for so long.

The biggest damage will be to Straight of Hormuz - of those drones can be used to hit Oil Tankers ... if there are enough muntions, it will be bad

All of that said, China and India would be super duper upset about that, and Iran may depend on China for parts. They would have 'no friends' at that point.

So it's all plausible.

But it requires Iran to have capabilities.

The entire Middle East is lit up right now - and that puts US forces on a 'clock' - this is going to be an interesting form of attrition on all sides, not a good situation.