No matter how strong you are, if they pull off a good attack they can wipe your entire party and you can't do a thing to stop it, because Atlus thought getting rid of Endurance was a good idea.
I mostly really like the lack of endurance here. About 90% of the time, this is my favorite turn based battle system. It's kind of cool to stumble upon a lvl 75 boss with a lvl21 party... and still win.
On the other hand, there's the other 10%. They really should have considered this limitation better while designing encounters. Making some boss battles randomly start with surprise attacks for the bosses can result in basically unwinnable situations due to the lack of endurance. And the random factor just shows how they weren't even worried about balancing them.
There really shouldn't be forced surprise attacks in this game due to how it works - the only surprise attacks should happen due to the player' own fault on the field - or maybe dialogue choices, not forced ones where sometimes you have to hope for a mistake from the AI. At the very least, if they wanted some first attack advantages for the AI at times, it should be scripted in such a way that they couldn't just wipe out the player there.
Also how do I fuse Ares? I'm having a hard time reading the fusion guide in the provided strategy guide.
You can't fuse Ares early on. You need to be higher level, in spite of unlocking him so early. Same goes to most early bosses. You get all these messages about unlocking them, but will need to get to around lvl 20 to start getting some.