You don't lose the output of the coasting team member (even if you get rid of the right person); that workload just gets transferred to the other 4 people. So let's say you have 5 people, 4 of which each are doing 22% of the work, leaving the one "coaster" to be doing only 12%. You fire the coaster, and now you've got 4 people doing 25% of the work each. An already burned-out team is now filled with people who have a larger workload.

And this of course is a simplification that assumes workload is a continuous rather than discrete measure. If the fired guy had two or three Jira tickets he wasn't making progress on, now you've got two or three of the remaining workers getting another entire feature dumped on their pile of work. The burn-out is higher than 3%. Until they quit, of course, transferring their workload to the remaining 3 people, increasing their burn-out, etc... it's a dangerous chain reaction.