That's not really the issue.
The issue is the inconsistencies between all of the jobs.
Some of them have levels, some of them don't.
Some of them are affected by worker potions, and some of them aren't.
Some of them require you to be in a PK zone, and some of them don't.
Some of them are affected by inventory limitations more than others.
All of these inconsistencies add up to the big differences in overall money made per hour for each job.
I'm going to pull together some statistical data about each job to illustrate this point. (I've done it before, but it was incomplete, and is now outdated due to changes in some jobs and my mining level.)
This was my old one:
My mining level was 9 at the time; it's now 25.
Casino no longer works.
Southridge increased the amount of money made by doing car missions because you could get $72 per mission.
Not to mention the gmap and speed and turning ability of cars changed.
And I never added bouquet making, woodcutting, or trash picking.
So it will be a very different graph when I'm finished updating it.