That is simply terrible accounting for variables. 80% turnover and you're like, "Yup. Same thing!"
You have a fundamental misunderstanding of what recency bias is, and it's evident by stating that 5 years is the time horizon commonly used to avoid it. There is no set time, as it can take a differencer of seconds for the bias to take effect.
If you want to breakdown the past vs. expected performance of the 4 remaining players, you may have the basis for an honest argument, but for the purposes of the argument that was made, that data must be discarded.