Not enough of room for aircraft to hide. Under 500m, they can be engaged by small arms, including heavy MGs, and under 2-3 km the MANPADs are a threat. JNA lost 25 jets by those means in 1991/92, against the enemy without hi-alt air defence that HAWK or SA-2/3 can provide.
Yes, integrated air-defenses are, well, integrated for a reason of one of systems covering shortcomings of another.
The text in blue is easy to fault.
Radar-assisted firing solution will start making firing solutions before the inbound aircraft enters the kill zone of a gun. So we have a gun firing at aircraft that is at 3 km, in order for the 1st burst to meet the aircraft well within the effective range.
Further, a bombed-up jet aircraft flying low and trying to find and bomb it's target will not fly at 800 km/h, but much lower speeds. Anything that try to avoid Vigilante will find itself in the net of the HAWK.