In reality, trying to measure software development productivity objectively always makes me whip out a little venn diagram that shows that what matters and what can be measured have but a small intersection.
But abstracting away from tickets, as a manager you set some kind of expectation for "the minimum." However it is you rate people from "not meeting expectations" to "meeting expectations" to "exceeding expectations," my contention is that it's the job of a manager to make sure that "meeting expectations" means that an employee's work is a net benefit to the company.
Whereas, "dead weight" describes someone who is a net loss to the company. So to me, someone who just meets expectations should not be "dead weight." If they are, I suggest there is a management problem.
That said I agree with the idea that someone that adds value that is some reasonable multiple of their salary gets to keep their job. If they're not adding value because they can't perform their job or don't care they should not keep their job. If they're not adding value because of how they're managed their manager should not keep his job. If this issue is endemic in the company that probably means the CEO shouldn't keep their job... In an ideal world anyways.