Your first lesson in Air Defence V1.01 would tell you that a large lumbering beast like this HAV would be vulnerable to fire from:
1. Pretty much any aircraft fitted with a gun(s) and missiles - remember sniping the engines or cupola (or whatever they've called it) would be the aim. Here is a picture of the tragic loss of the Goodyear blimp, filled with Helium I hasten to add, that had a fire in one of its engines I believe?
2. Any ship with a big enough gun (like the RN's ubiqitous 4.5" gun that can hit targets at 15miles away up to 40kft) or a ship launched surface to air missile system could whack this lumbering beast at 20kft with ease.
3. Small vessels with MANPADS capable of reaching the HAV's altitude.
Every man and his dog that can get something onto the HAV would have a go. Being a High Value Air Asset, then the AEW capability would feature as one of the first aircraft to have a go at. Don't get me wrong, Crowsnest would be just as valuable a target for a Fleet attack - it's just a lot harder to spot visually or on radar plus its a damn sight harder to bring down than a massive great behemoth like HAV.
I would suggest that trying to use a HAV in any defence related role without total Air Supremacy would be a massive tactical and strategic blunder. We just don't have enough F35s and Typhoons to provide Air Supremacy for HAV to oprate in. Furthermore, flying escort and sweep for such a massive behemoth with such limited capabilities is not a smart use of high-end air dafence capabilities.
By the way, I always thought the use of the words 'blinkered thinking' as the epitome of
L'esprit de l'escalier...
The B Word