Its better for the same reason that the 88 on a tiger is a better anti tank gun then the 25 pounderartillery piece(also 88 mm) Higher velocity from a longer barrel and a larger charge.
The 88 keeps its velocity a bit better because of the superior diameter to weight ratio of the round. Or so I read once..that 88-90 mm was the ideal balistic caliber for a full caliber round..(discarding sabot changing that of course)
