Zooming Fliers can fire four weapons.
Vector Strike does not require you to sacrifice the firing of a specific weapon, and is in fact an additional form of attack, which one can legitimately call a weapon in it's own right.
Why are you sticking to this so rigidly? Everyone you've asked so far has explained where you're going wrong.
Let's see if a different approach will work.
I can field a flying Hive Tyrant with absolutely no ranged weapons or psychic abilities. Therefore, having no weapon to substitute for the attack, according to your logic, it cannot therefore Vector Strike either....