The game is relatively difficult, but I don't find the combat simulation to be a good gauge, you won't ever fight alone and while the AI is derp derp at times, if you have them set with Cure they will heal you fairly often so you don't have to heal yourself, plus they also kill/distract stuff, and there's no permanently spawning enemies besides boss fights, you fight for a little while then it stops and you can heal back to full, while the simulation just keeps going forever.
That said, mastering each playstyle you can definitely last for a while, and with some of them you can last forever once you unlock specific skills that give you sustain(for example Sice has an aoe that drains life and only costs AG, making it very easy to live forever as long as you're not getting crushed).