Because Lebron makes role players seem better than they are and makes players that often require the ball look worse. Ingram looked fine towards the end of last year and as he gets more involved he looks fine again. Kuzma is a great scorer and does well alongside Lebron, he is not nearly effective sans Lebron nor he is a capable defender. Literally all the guys you listed to trade are our best defenders outside of the bigs. Do you want us to be Cavs 2.0 or something because Rondo/Beal/Lebron/Kuzma/McGee ain't defending shyt.
And stop with the Lonzo slander just because he doesn't score. Do you think we need more scorers on this team? More guys that need the ball in their hands?
Again I don't want to be the Cavs 2.0 and yes I do think there's reason to believe Lebron declines as he ages because all athletes do and eventually others will have to do more and that means not relying on him to set them up all the time. As he ages his defense will also get more lazy, again meaning we will need defenders to shore up for his lazy possessions.
If Beal was a Harden time I'd be fine with it. If this was Kawhi then I could live with it. He's not that and I'm not giving up the future for Beal so we become slightly closer to a contender but not a real one as he doesn't push us over the edge anyways.
