I think the case that Lebron had a decent supporting cast is legit. They may not have been all-stars after going to CLE, but next to Lebron in Mike Brown's system, that was guaranteed due to the no-motion, one-option offense.
The thing is, he didn't make the guys around him look any better. Despite those winning seasons, no Cavs player I know of was a desired free agent anywhere.
He didn't make anyone look good but himself.
And when it came time when he couldn't win by himself, he wondered why the team didn't play better...well, of course they didn't. A roster can't stand around and watch Lebron from October to April, and then suddenly run an option-offense that incorporates other guys, especially if Lebron has the ball all the time.
The Cavs might have fared better with a different coach, but...
...they still would have run into the 2006 Heat, 2008 Celtics, and Lakers of the past couple of years. There was just no chance for the Cavs to really win it all. It wasn't his time.