Not personally knowing either, I'd say they seem to be very different personalities.
I have always rated Valtteri as a very good 'thinking' driver....Prost.like.
He will get what he can out of the car on days when it is good.
Lewis is just simply 'quick' right out-of-the-box.
Some drivers just have that ability...coupled with a mental toughness....Clark, Senna, Fangio, Schumacher....and now, Lewis.
Those guys can wring the neck of any car to put it in a position most can only dare to dream of.
That is why he is paid so much and allowed to go do his 'thing' when away from the track.