He has benefited from a historically weak conference.
His 2007 Cavs team was horrible. Probably would have been the fifth best team in the west that year behind Dallas, Phoenix, San Antonio, and Utah.
In 2014 the Thunder and Clippers, were arguably better than the Heat. The Spurs obviously were. Heck, even Dallas, which had injury problems the whole season until the playoffs, gave the Spurs a really tough 7 game series.
In 2011, Oklahoma City was also really good as they had Durrant, Westbrook, and Harden. Dallas beat the Heat in the Finals, but OKC could have arguable done so as well.
Bottom line, if any of Lebron's teams had been in the Western Conference, there's only three years where they would have even gotten to the Finals.