How much more developed would Kim be if he started out as the eager, young, "momma's boy" ensign before having to deal with the realisation that he'll never see them again, the emotional fallout alone would make him a sympathetic character--not to mention the possibility of self-destructive behaviour he might take on to deal with it (he's set himself up to be the perfect officer so turns to stimulants to keep up with the impossible level he's set for himself).Finally imagine yourself trapped on that ship seventy years from home, with people trying to blow you up every other week, your ship taking a pounding, limited supplies etc.. Are you really saying that it would never get to you the fact that you might never see home again? They never really sold us that these people might never see their homes again, sure the writers knew they would but the characters wouldn't know that.
Or Chakotay actually taking a different stance on situations and not just being Janeway's "token Maquis"? Actively working against her at times to make the lives of the crew better. Ramp up the tension between them and actually give them some conflict.
They could've given bland character a little depth and interest to them.