I take your point that there is a limit on meaningful activities one can undertake but I disagree that it's some kind of zero-sum situation. I used to find my work more meaningful and I don't think it made any other things less meaningful - I just felt that I spent more of my day doing things that meant something to me. Life, on the whole, can feel more or less meaningful; we don't distribute a fixed amount of meaning across all the things we do.