Slightly softer rubber but just different tread pattern with sipes not bigger gaps and the summer tyres only lasted me 10k where as the all seasons have done 15k, I think that the little bit more compliance from the slightly softer rubber allows for more movement during set off, braking and cornering(it’s very slight) where as the summer tyres with the harder rubber tend to drag more and break traction more easily even if it is just fractionally it seems to eat through the tread faster.
I have about a dozen friends who have gone this route over the last 5-10 years and all get the same results and all said they will never go back.