I literally have this exact same problem with my traps as well. I don't really get depressed, I just get extremely irritated, especially after a workout where I can tell that my left trap is pumped and looks huge compared to my right one and it just pisses me the fuck off. It just sucks that you work so hard to develop a solid physique and yet your body doesn't seem to follow the same roadmap that your mind set out for it.
For those saying just gain more size overall, wouldn't more size just lead to a larger imbalance? For example, if one of your traps is larger than the other, or one of your pecs, or your shoulders, etc, wouldn't gaining more size just make the imbalance between the two uneven muscles more pronounced? I know there's probably different opinions on this, but just wondering?