While some of the pilots only had very rudimentary training, they had several things in their favour.
1) WW2 planes were more durable and generally better protected - armoured windscreens and seats to protect the pilot.
2) In the Battle of Britain, both sides used a lot of machine guns and fewer cannons compared to later in WW2, so the armour was relatively more effective
3) Unlike in WW1, WW2 pilots wore parachutes
4) The state of knowledge of flight was generally more advanced, so I would make the arguement that Spitfires and Hurricanes are much less treacherous than Sopwith Pups and Fokkers
5) British pilots flew over friendly territory where medical aid was much closer than over the moonscape of the trenches
6) As planes became more advanced, much fewer were flown/fewer pilots were needed. The production rates for WW1 fighters is simply staggering
7) German fighter pilots over the UK were extremely fuel-constrained, so had fairly deliberate objectives: Fighter sweep, escort bombers, etc.. They didn't simply prowl around looking for random air patrols to ambush like happened in WW1
8) Radar and the rest of the air defence network infrastructure and better C&C in general, as well as the proliferation of radios generally gives WW2 pilots a degree of situational awareness not possible in WW1
