Today's Torygraph has a snippet about Typhoon and Brimstone:
"The unexpected campaign against Islamic militants" sort of says it all.
Decisions made decades earlier are no more than a blind guess. Maybe, like a true MRCA, like Nimrod, all bells and whistles should be designed in but not necessarily procured or fitted.
That Typoon was procured with a gun bay and guns were cheaper than ballast was fortuitous.
Back to guns, during Confrontation, it could have fallen to the Javelins, Sea Biden's and Sabres to warn off intruding Indonesia aircraft. Using a missile would have been problematical and not achieve the political aim.