Nothing is unchanging though. By that logic you have to wait at least 10 years to evaluate players in a draft because at any given point they could turn it around and that just is a nonsensical way to look at it. Geno Smith was a bust. Now he is a good player. Zach Wilson has been a huge bust but he could turn it around. The same is true of Josh Rosen.OK, and that's where we disagree. A "bust" isn't changeable. You either are or you aren't. There's no "well maybe they'll turn it around". Its definitive or not at all.
Conversely that would mean that no player can be called a success because they might suddenly get worse. A far less common scenario but not unheard of (Ezekiel Elliot being great for 2 years average for 1 then just dropping off a cliff comes to mind). Therefore using your metric you cannot discuss or evaluate any player because at any given point they can change because they absolutely will change. Whether it is for the better or worse is unknown but they will change so any discussion of players is pointless.