I believe your definition is correct.
I believe claiming there's a substantial divergence between yours & theirs is incorrect.
I think of malum in se as intrinsic evil, your examples are as good as any.
Think utilitarianism. Parking shouldn't be a problem. BUT !
Parking in the middle of an otherwise busy intersection can keep workers from their jobs, ambulance patients from life-saving rescue, etc.
Parking & blocking a fire hydrant may seem harmless enough with no conflagrations or fire trucks in sight.
But leaving firefighter access to the hydrant benefits society.
For me the obvious malum prohibitum example is Drug War.
It's bad because we say so, even though for most of human history there was no such prohibition, and we did just fine.
Nemo Est Supra Legis: No one is above the law.
The ancients were not stupid, they were technologically primitive.