What level are you, roughly? IIRC after that particular event, the game opens up basically all of the endgame content as well as the rest of the story, so you're sort of intended to do a lot of side questing and level up a bit. But, and this is important, you can beat the game WELL before grinding into the high levels and doing a lot of that optional content. IIRC the final boss is around level 80, while there's tons of stuff in the game that's well into the 90s and beyond for postgame. Certain areas like the new sections of are more intended to be done after beating the game, not right now.
Of course, turning on casual mode to finish off the game is totally fine, nothing wrong with that! I just wanted to mention the structure in case you were trying to go for a lot of the stuff that's more postgame-oriented.