There is a huge difference between high performing senior engineers, and high performing junior engineers.
But lots and lots of senior engineers aren’t high performing. They’re still moderately more valuable than junior engineers, but not immensely so.
People calling themselves “senior engineer” are usually referring to years of experience, not to whether their management chain consisently sees them as high performing.
Also that senior engineer can be high performing in one situation and not in another. And it is not always about the job. Some trouble at home and can't sleep well? Not going to be a top performer for long.
What I mean is that it is hard to give a number to a person. Sometimes they shine, sometimes they don't.
But lots and lots of senior engineers aren’t high performing. They’re still moderately more valuable than junior engineers, but not immensely so.
People calling themselves “senior engineer” are usually referring to years of experience, not to whether their management chain consisently sees them as high performing.