The Beaufighter wasn't far behind the Blenheim in terms of the war, introduced 10 months after it started. It took some time for reality to be forced on those buying planes, bombers and other aircraft needed engines as powerful as fighters and you cant just specify more crew than you actually need because it seems like a nice idea. For me, with the engines used the Blenheim had no chance of success with a three man crew and the Hampden and Beaufort even less chance with four crew. The extra men, space, fuel and equipment are equal to a pay load.
Even if we get the Blenheim down to a single crew member - pilot - it will be a bad fighter. It was too big & too draggy.