As a 'developer' I thought 'we were doing all the stuff' while everyone else catered to us.

During my roles out of that seat, I view 90% of development as a form of intellectual labour, it's just work, one piece of many things.

The hardest job by far is selling.

The next hardest job overall, as the commenter mentions, is making a 'whole product' and targeting it at customers.

Engineering is hard, but not harder than the above.

I would almost like every Engineer to work for 3 months in PM or Sales just to get their perspective flipped.

Engineering feels more 'worky' because it's more direct.