Should try fighting him without the summon around the 40s. It is a good challenge, took 25 minutes, but I killed him. But he's horrible exp for having 500k HP. Immunity to status effects is like having a ribbon on, it'll probably be in game, you'll just have to get some really great food to achieve it. But this is a demo it is representative of their game. Some things were tweaked for the sake of the demo, but systems shown off will likely all be there just with more content.

But if you've been watching the videos I posted here, even before the demo arrived you should have known about nearly all of this. They explained very clearly how combat would function before the demo released. So my expectations were already adjusted with what was being delivered. The only surprise was Ramuh.