I should have specified a little bit more, but I'm assuming the answer stays the same even if I mention that I will be doing lots of cardio from full court basketball like 3-5x a week 1.5-3hrs each?
With that kind of schedule putting on any appreciable lean muscle mass is pretty tough...or at least beyond newbie type gains. But there's a pretty big variance in there... I think 3x/wk for 1.5 hrs is do-able... 5x/wk for 3hrs chances are slim.
So does this mean, as long as you have your core strength up to a certain degree where you are able to have pelvic control and core stability during athletic movements, any more training will not lead to any more athletic gains, directly or indirectly?
If that is so, is there a way to know if my core strength is good enough to the point where I have solid core stability and pelvic control?
I've never heard anyone complain from having a core that is too strong. Might as well continue to progressively get it stronger. Doesn't have to be really time intensive and it can only help all future athletic endeavors (and help prevent injury).