I don't think you were being whiny at all, it's just that the point itself has been driven to death over the years. Pretty much everyone claims that Zero is the spotlight-stealer. And, quite frankly, sometimes they're right. In the case of X4, they definitely are (although part of that may have something to do with it being Zero's debut as a fully playable character, but X's lack of cutscene time is hard to excuse). But most of those people tend to either dismiss the good points that X did receive, or in the case of X5, grossly overestimate any benefit that Zero is alleged to have obtained from the extra focus.
Oddly enough Zero's best character development in X5 is probably the alternate path where he is removed from player status. At least that way it explores the idea of his "mission" and Wily's intentions. The "canonical" path of X5 does absolutely nothing to strengthen Zero's character, in fact he is noticeably more of a hardass in X5 than in most other titles (seen in his dialogue with Dr. Light a few times). The game as a whole doesn't really do Zero's fans any favors, either. A player who botches up on their first time through and is therefore punished by having Zero removed from the roster and killed is in for a very rude surprise when they're motivated to shoot for the better ending only to watch him die a cheap death anyway.
X6 I feel struck a good balance between the two. Again, Zero may be the source of conflict, but he's also optional as a player (which contrary to popular belief, X is not in X7), and both he and X get some pretty meaningful dialogue. X's in particular is interesting because we get to see how he reacts both to a personal threat and to a seemingly impossible one, the latter being something we almost never see outside of X1.