Goddamn this is idiocy. Bron wasn't GM at all for the first run Cavs (and they were just as bad when he got there as when he left), that leaves:
Heat: 4 Finals appearances and 2 rings in 4 years, when he left the starting lineup was solid with Dragic-Wade-Deng-Bosh-Whiteside, that core fell apart due to injuries but they retooled and were back in the Finals 5 years later.
Cavs: 4 Finals appearances and 1 ring in 4 years, last year he was there he didn't get to have a say in any of the trades because they were retooling for the future and they've done a decent job of building back up.
So what team did he leave in shambles? He's literally gotten a ring with every team he's been on, if there was a GM who had built 4 different championship rosters on 3 different squads he'd be in the Hall of Fame on the first ballot. Of course LeBron has a cheat code because he's managed to win rings with deficient rosters, but he's certainly not a "bad" GM. I'd say he's about an average GM, which is pretty fukking amazing because all the others are doing it as a full-time job and for him it's just the side gig.