Hmm... I can't really say that game has a lot of tough bosses. I think I died once in a optional boss fight? Jr. vs Joe? But that's because I never saw it coming, and I was way too weak when I fought him.

AGWS wasn't all that useful at this stage, because they'd be too slow. And you know you're biased for not using Kos-Mos. Kos-Mos deals out the most damage, until Jr. joins. And Jr. will be the king of random encounter by then...

Still, in a boss battle, I found that Kos-Mos is most well-rounded character. With the skill transfer, she can deal out tons of damage, self-heal, and can take a lot of damage.