Yeah, Burnett's a classic mama's boy, all hat/no cattle type. As you pointed out, he was the shortstop and he was the one who suggested that Mitch leave through the outfield to spare the others (but let's be honest, himself).
Not only is the smashing the beer bottle/being a lightweight theory spot on, but his false bravado towards Hirschfelder about leaving the dance early was not only a bad friend cockblock, but steeped in the jealousy of no prospects for himself.
Here's the reality for Carl though--he was likely the king of middle school due to his big mouth and false bravado, but his friends are going to start seeing through his shit and not tolerating it at HS, especially with Mitch's transformative, legendary night with promises of greatness ahead (like Jordan's 63 in the playoffs against the Celtics) and Mitch will be a much better hang than Carl. Pink and his crew will tolerate most of Mitch's boys, but Carl will be too entitled and mouthy (and he'll always wear the yoke of his Mommy pulling the shotgun to protect him) for the upperclassmen. Bye bye Carl, and he's too scrawny to even warrant O'Bannion's worth on the football field.