IMO, a lot of people using LeBron's Finals record against him is based on an assumption about MJ. That if he hadn't left to "pursue his baseball dream," he would have gone to and WON 8 straight championships. He book-ended those two years with the two 3-peats, so it is probably assumed that is what would have happened, therefore MJ is clearly the greater player.
The counter argument that LeBron never had a Pippen/Grant or Pippen/Rodman combo to play with is more valid, IMO.
All that said, I still think MJ is the GOAT, but LBJ is clearly #2 at this point, just 'cause.