SJ is definitely designed like a Megaten game in the sense that while it starts off pretty tough, as you familiarize yourself with the fusion options, and the combat mechanics, you will start to build really good demon teams, as well as backups, and it becomes much easier. On a whole the game is much "easier" than EO, and rewards the player significantly for building a party which is good at attacking weaknesses, as well as keeping in the same alignment to take full advantage of Devil Co-Op.
The game is definitely designed such that as story events change the main mission, you can keep playing and experience the scenario without turning the game into a draggy grind of going back and forth between the dungeon and the ship just to make small steps of progress.
That's not to say you won't die every now and then, especially if you're careless or you encounter new foes your party build might not be equipped to handle. But such deaths are not something you have to grind to overcome, but simply requires a change in strategy. There are quite a substantial number of save points throughout each dungeon, so that's another thing that really helps the pacing.
