No, it sounds like there are clear differences in abilities.
If you think every junior/senior/staff has the same ability, you're delusional. Two people can broadly fall into the same bucket but be very different in terms of output.
Yes there are clear differences in skills. So if I'm hiring to fill a certain need, why would I consider someone who isn't skilled in that area?
I often look at a CV and notice specific skills that can benefit the business even if they aren't part of a normal job description. Imagine a software developer who used to be a graphic designer. I can save handoff time and have this person take on additional tasks, but it won't be in the job ad because the hit rate is too low. I can afford to pay that person more than others with comparable programming skills.
Or, I find value in areas that get overlooked in the market. Career transition people for example might not have many other options and I can take a gamble on how fast they ramp up.