Concentrated 20mm fire would make mince-meat out of anything flying.
MP - the Stuka was used for so long because there was nothing to replace it. If you note, it was withdraw from service over Britain well before the BoB was over and had virtually disappeared from service against the West by 1942 (the exception being the night-flying Stukas). It only enjoyed any sort of prolonged success over the Eastern Front where the Luftwaffe maintained superiority longer than anywhere else.
The Helldiver is probably one of the most maligned aircraft of the war. The early version did have problems, but the later versions -3,-4,-5 more than made up for them. The Helldiver sank a greater tonnage of Japanase shipping than anyother aircraft.