Regarding Uhus; a more valid measurement of the effectiveness of the Uhu vs the Mossie as a bomber destroyer is: if 500 heavily laden Heinkel 111s flew in loose connection from Germany to the UK, how many would be should down by an experienced Mossie nightfighter crew?
But perhaps the real question should be: why didn't the Luftwaffe take the air war to Bomber Command? Infiltrate a few JU88s into the stream back to the UK and lurk over the airfields; tired bomber crews, aircraft low on fuel, airfield landing lights etc.