The point is a wizard has a whole bunch of ways to bypass the chance based portion of any given challenge, a fighter and a wizard want to get past a stone wall, a fighter has to make a probably very high skill check if not multiple and that’s if the DM doesn’t just say ‘no it’s just too hard to deal any significant damage to it’, the wizard can just say ‘i cast stoneshape’, or passwall, or dimension door, or stone to mud, or disintegrate, or any other number of spells they have available that don’t require a dice roll