Yeh but since when will a seasoned Me Bf 109 pilot put his 109 into a dive from 6000 feet to reach 450 + he wouldnt as he would go straight into the ground 
He needs only ~350 to match the mossie on the deck. Practically all WWII fighters will be able to do that. The problem is to happen to be close enough to visually see something flying at 20feet when patrolling at 6k - not so easy. WWII fighters have a huge blind cone under them. To see something close and much lower they have to keep dropping a wing and look down. Unless the patrolling aircraft knows that there is a target nearby and is actively looking for it, the pilot is not likely to keep this up the whole patrol time.
Mossie daytime missions were rare and heavily counted on surprise - that means that there will not be a 109/190 patrol looking for them, in particular not the latest models that could outrun them. The K4s/D9s and their late war brothers would not be the typical LW fighters that a daytime ranger mossie will run into until perhaps very late in the war. On top of that, conditions of low cloud cover were favored for such missions, offering an escape into the cloud layer, where the speed difference was small enough to buy the mossie the time to do that. The 400+ mph mossies were high altitude variants that were flying almost exclusively at night. Very few night fighters were fast enough to catch them and in that case, flying 6k higher and making a diving attack is not an option at night.