I don't understand the logic behind one player carrying a defense. In basketball these days, with the way spacing is, and with the way the players are the most athletic as they have ever been, good/great defense takes all five men on the court accounting for one another. This isn't 1963, where one big man in the middle can dominate and negate most of the opposing offense of non-athletic, short players. There's no excuse for a player, like LeBron, to get a pass to rest on defense. He's skill-set and level of play on both ends is too important to his team and it's success.
For one, he's extremely compe ive, so he wouldn't even think about resting on the defensive end in a relevant regular season game or playoff battle -- win's are too important to him. 2) He's a leader, he knows that. Therefore players feed off the energy (defensive or offensive) he brings to the court-- it's a case of "leading by example". The best players in the world should always feel responsible on both ends of the court. IMO
Do the Cavs need more help? Sure they do, especially on the defensive end. However, we don't know what other moves they plan on making and we don't know the defensive ( compe ive) potential of Kyrie or Love or any other Cav (besides Andy), considering they have all have played on crappy teams their entire career-- which inevitably leads to more "careless" play (especially late in the year).