I think they slightly overdid it with the vocal songs, yeah. FFXIII had the perfect amount. When there were vocals, they were enticing and refreshing, like areas such as the Sunleth Waterscape and Oerba. Here, it's a bit much. Also, I'm not a fan of the heavy metal/super rocky themes that plague nearly half of the soundtrack. All the other tracks are pretty epic, though. I love Hope's theme here, even better than FFXIII's. :3
The OST in FFXIII-2 seems to suffer from the Crisis Core syndrome. Half of the tracks are beautiful and orchestrated, and the other half are bland rock tracks, with no feeling in them at all, save for a few.
As far as the battle theme goes, the violin saves it. Which one of these is the "real" battle theme though? These two tracks both have the violin bit, but I'm not sure which is real. Also, the first video shows up in the OST tracklist far before the second, last I checked.