Brave words for someone not there. Imagine if the Iranians got the drop on the party by training and cocking a few large calibre machine guns on them? Imagine a scenario where the boarding party commander went to speak to the Iranians and was held at gun point?
Would you still go down fighting if one of your guys was being held at gunpoint?
You make a valid point: the larger craft could sit back out of small arms range -- and hose the inflatables with, say, .50 cal fire all day long... No contest!
The bigger question is why didn' the Cornwall help our her marines in the rubber rafts when they saw the iranian boats approaching? It is even possible that one of the best equipped, modern ships on the high seas somehow "missed" the approach of the Iranian vessels? Those Iranian boats had to have been tracked for a long time, long before they overran the Royal Marines in rubber rafts. Just how far away from the mother frigate do you think those rubber rafts were? Something really stinks here.