It took him 8 tries to get the finals and win just 3 times, he's not winning 3, he'd be lucky to win 1 at that rate.
His last le took GS exhausting themselves, chasing 73 wins, a Curry injury, a Bogut injury, Green suspension, and them only having 3 days rest in between a 7 game series with OKC and the finals where they ultimately collapsed from exhaustion. Meanwhile Lebron had his usual regular season cakewalk, and eastern conference cakewalk against the Lowry-DD Raptors & a week off before playing GS.
His last championship in 2013 was the result of an exhausted Parker's hamstring giving out as well, so already 2/3 championships were the result of him playing in the East.
You talk about rest but there is no rest in the West, you need way more wins to reach the playoffs (Lebron's Lakers this year would be 8th in the East), each loss means more, each loss creates drama in the locker room, each loss puts more pressure on you and Lebron can't handle that. He's been on super teams the past decade, surrounded by really good cores and even role players/vets that took pay cuts to play with him and was still underwhelming.