You're taking this too defensively, how would they show Crono screaming out in anger? With a sprite. How did they show Crono surprised. With a surprised sprite.
Crono doesn't have as much of a history as Serge, I'll give you that, and the resources for CT and the resources for CC weren't exactly the same, so without dialog they don't have the same ability to convey emotion. But if you think that Serge had better character development that's fine, personally, I thought that they developed at about the same rate. Both had their heroic feats. Serge, however, did have a deeper story and was a bit more tragic overall, but he and Crono progressed at basically the same rate.
Emotion doesn't mean character. History doesn't mean character. Action means character: it's the action the characters take that represent their character. Crono chose to go save Marle, Serge had the option to save Kidd when she was poisoned, but his "quest" was simply one he was thrust into.