You're taking this extremely personally. My comment is about a scientific paper, not about you.
> Well, it's a profession, so yes.
I meant from a scientific perspective. I.e., here's the point: "can we lump all programmers together, randomly sample, do a correlational study or survey, and draw conclusions about the underlying population?"
I assert that such studies will generally fail to replicate and will mostly tell you about the properties of a skewed convenience sample.
> They both write code all day. Professionally.
You could say the same thing about people who work in hospitals. Or people who work in offices. What's the difference between a novelist and a listicle author? They both write all day, professionally.
Heck, what's the difference between a journalist and a lawyer? Again, they both write natural language all day. Professionally.
And sometimes you can do studies that generalize. But, generally speaking, an empirical study about what makes novelists productive won't necessarily tell you how to make legal clerks more productive.
It's not income. In fact, I didn't even mention the salary of the senior engineer in my hypothetical! $FANCY_CO was supposed to be a sign-post for difficult problems and/or complex politics, not compensation. (The $10/hr web dev does sign-post the complexity of the work, and wasn't meant as a hyperbole... I started my career making $10/hr doing PHP dev for local businesses. It was really easy work. Requirements were simple, code was trivial, and there was never more than 1 counter-party. The job was low-paying for a reason.)
It's the type of work. I've done a lot of programming, of lots of varieties at nearly all pay scales. Here are some buckets:
There's a lot of programming that is easy and mechanical (at all payscales). There's a lot of programming that is extremely complex and requires intense symbolic/mathematical reasoning.
There's a lot of programming where the code is simple but you need to think long and hard about some complex technical topic separate from the code.
There's a lot of programming that is extremely social and requires an incredible amount of intentional interaction with customers or internal stakeholders.
These are the same job in the same sense that all medical professions are the same job or all people who write natural language all day have the same job.
There is a strong relationship between pay and the degree to which an inebriating drug would impair your ability to perform well. But it's of course not a perfect correlation. Some highly paid people do trivial work. Some low paid people do complex work.