Poor Sharla. It's funny because I pretty much felt this way. Every character in the game was amazing to me, except for Sharla who, while I respected her personal struggle and wanted to help her out, just kinda felt like she was...there, the whole time. Still good, just like everything else in the game, but just...there, compared to the rest of the cast. I was even more involved with Mumkhar, Egil and a certain spoilery major character than Sharla.
On the topic of trophies, series like Pikmin and FE had a bunch of random things chosen for trophies. If Xenoblade doesn't get at least the other PCs as trophies, (hell, I'd be surprised if Dixon, Mumkhar, Egil, the three obviously important beings, and some others didn't get trophies.) The main characters are a must though, an absolute must.