I understand what you're saying. I can keep up with the players manually, it's my AI teammates that can't. When I guard LeBron one v one with Caron, it's usually pretty good, except some plays he blows past me when I'm supposed to have DeAndre or Blake ready to move in front of the basket to alter the shot. Not a uncontested dunk.
As far as teams who spam the 3, I'm good at guarding that as well, except there's instances where someone manages to have Novak/Melo (Whichever one they have at the 4), manages to get open and Blake is still around the mid-range area. It's frustrating when I don't give up the 3, my teammates do.
Maybe I just need some suggestions on how the Coaching Sliders work or how to switch players fast enough. Those are my 2 main problems on defense. One on one though, I'm usually pretty good.