The developer made a tool which let Jobs rapidly iterate through a number of ideas until he saw what he liked. There's no reason to believe he knew what he wanted until he could experiment in a low-friction manner for himself. That's what the dev gave him.
You can't iterate through something without parameters and do the same. Look what happened to me: http://i.imgur.com/rCHiZyR.jpg
No one is going to argue he wasn't a rampaging narcissistic asshole. Even so - it makes no sense at all to ignore how much he steered the look and feel of Apple products, and of late 20th/early 21st century design in general.
He was the only person working in computing with a consistent interest in design. Microsoft and IBM had zero interest, DEC had a minor interest in making nice-looking minis and mainframes, and the 8/16 bit micros often had some product design applied to the casing.
No one else was thinking about software and GUI aesthetics at all.