I own an sl and heritage in 155 and have rode the proto. The proto isn't really softer than the sl in practice - just far less damp.
Agree. But dampness is part of 'going up' the scale.
The heritage, while stiffer than the sl is fine for park. It's not any good for presses but its better on jumps.
Mostly true, but most people would consider the SL to be the better park board. It might lose out a bit to the Heritage in the jump line, but is way better for jibbing.
The heritage is a better 'all mt' board for me because it charges way harder than the sl. Way better for busting thru and over chop.
Most people would call that big mountain/freeriding. All-mountain includes that, as well as park, etc.
I prefer Heritage as well, but the SL is clearly more of an all-mountain board. On balance, the disadvantage the SL has in charging is smaller than the advantage it has in the park.