Its one of the most over look attribute.
stamina + exp = 4th qtr comeback & stableness
Here is my wild assumptionevery stamina worth 4 minutes ofgood play(2 very good + 2 OK), overplaying him u see his subpar game and i guess all his skill lv drop 1-3 lv in the time being.
and for those who think freq sub in and out can solve the problem:the coach has to see a bad play and wait for dead ball before subsitutionso that player is the weakest link if ur opp try to exploit.
But in the end i will say you are right, i play long time with a average stamina below 4 with my team, and didn't see crashes in the 2cd or 4th quarter more then my opponents, and i know that some of them train it from time to time. And even my stamina 1 guys, sometimes make good final minutes.
fact - stamina is more important when you play haste tactics (look, push, run) than slow tactics.