You assume that learning ability is a zero sum game. I believe (and observe) that this is not the case.
Time IS of finite amount, however. Human brain is a beautiful tool, whose greatest strength is correlating abstract unrelated information. I believe that levering that makes learning a non-zero sum game.
I have a lot of varied interests (beyond computers mind you) and I'm always amazed how improving on one field actually positively impacts others - seemingly unrelated activities.