Would a 40 mm Crusader have reset fighter armament?

If the Crusader had succeeded in Vietnam with 30 or 40 mm cannon, would later combat aircraft have retained weapons of that calibre?

Probably. Governments might have treated the heavier cannon as the visible cause of the F-8's success and carried that requirement into later fighter programmes.

The question poses a procurement counterfactual rather than a claim about what happened. If the Crusader had carried a successful 30 or 40 mm cannon in Vietnam, governments might have credited that weapon for the aircraft's survival and combat record. That interpretation could have hardened into a requirement for later fighters even if manoeuvrability, tactics, and pilot employment were equally important. The thought experiment shows how wartime lessons can create technological path dependence when institutions isolate one visible feature as the cause of success.