> It's quite likely that in about 5 years most military installations will have a mix of weapons to intercept those systems - and depending on a number of factors you could easily end up back at low performance drones being so reliably intercepted as to be a waste of munitions to deploy.

That's unlikely. Anti-drone defences will only improve, yes, but autonomous drone swarms numbering in the thousands to tens of thousands are doable today, and few weapons systems can handle the rate of launch/fire required to combat that. Especially if there are follow-up waves mixing drones and heavy missiles against which your anti-drone defences wouldn't be enough.

> WW1 after all was based on exactly this thinking: surely the volume of an army would overcome the machine gun.

But building a cheap kamikaze drone costs much less than building a human.