I agree... to an extent. Anyone who thinks Lebron is a "choker" is probably wrong. I just don't think we know how to quantify that, and qualifying it requires psychic.
On the other hand:
1. Lebron has clearly NOT taken his game to the next level. His foot work is not great, his outside shooting is mediocre, and his foul shooting is closer feels more like Rondo's than Pierce's. These are all workable areas - in fact these are all things Pierce has gotten much better at over his career.
2. Lebron says things that are stupid: "worldwide brand", the decision, "gave us a chance". He betrays a lack of caring about his craft, supported by number one, that says: I accept my physical gifts make me great, and feel no need to improve further. It's like big baby staying fat, but much worse.
3. He does keep losing important games. Fairly or (in my opinion) unfairly he will be held accountable for those losses, because he is the best player on his team. Just like Pierce was blamed for never delivering, until he did. The difference is that Lebron has talented side kicks in Wade and Bosh, and so his excuses are weak. (He cannot really say "bad chemistry" - he chose this team and destiny, he cannot really say bad coaching (never a good look), and he is the guy who is supposed to create.)
Lebron is a great player and I think good enough and young enough that he will win a title - and when that happens, he will be seen as a top 10 guy, and maybe even on the all time starting five, but for now, people love to see greatness fail and watch hubris in action as much as they love to see immortality through success, maybe more.