1. There is no such thing as PAC-3 in itself.
Patriot defense system can be equipped with PAC-2 class interceptors (M901 configuration), or PAC-3 class interceptors (M902 configuration), or both (M903 configuration). M903 configuration is latest and not commonly deployed
yet.
Patriot defense systems in Saudi hands are equipped with PAC-2 class interceptors on average to neutralize incoming ballistic missiles from Yemen (and Iran), and they have absolutely delivered in this respect; 100+ kills since 2015 which is very impressive.
Patriot battery stationed in
Mecca is equipped with PAC-3 class interceptors (M902 configuration ???), but this configuration is not confirmed for others.
However,
all are/were pointed towards Yemen because KSA and Yemen are at war since 2015, and majority of attacks are expected from Yemen consequently.
Not surprisingly, Patriot battery stationed near Abqaiq oil field, was also pointed towards Yemen. Abqaiq oil field was therefore struck from a different direction:
That is why the attack succeeded, and Iran's involvement is suspected.
French-origin defenses were also stationed there, and failed. This might be due to poor and/or disrupted radar coverage in this sector since Abqaiq oil field contain numerous parts that undermine radar coverage.
There are also reports of Saudi negligence in managing defenses surrounding Abqaiq oil field - radar systems not being active.
2. KSA does not have THAAD in its possession so I am not sure why you mentioned it.
THAAD is also designed for big-game hunting (strategic applications).
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KSA needs to invest much more in its defenses, address its operational negligences, and concentrate on Iran.