The lack of understanding is hilarious. If you seriously think LeBron can do what Draymond does on defense at this stage of his career, I think it's time for you to be watching more Warriors games. Stop thinking "wear and tear" only comes from guarding
dominant post play - just because you don't think there isn't any dominant post play 4s in the league doesn't mean he wouldn't be needing to guard and exert energy in the post. Furthermore if he was playing the 4 he would need to be the most active player on defense as he'd need to help on PnRs, running 4s off the 3-pt line, providing help defense all over the court and generally banging bodies with bigs in the paint. LeBron doesn't want to do all that extra shyt with all his mileage, and you can't really blame him since he's trying to extend his career as much as he possibly can.
Half the reason he went back to Cleveland is because he didn't want to all that dirty shyt anymore.