Big difficulty spike in final boss of three houses. Spoilers

I just finished the edelgard route, three houses was the first fire emblem game I ever played and I went in on hard right away. I'm not sure if I was approaching it wrong or something, but I tried to group all my units and March it right up to rhea. The game flat out does not let you do that. Black eagles does not have a lot of natural flying units and I ended up having no fliers in my team. Then rhea decided to set the whole town on fire, thank you. Not only was this a dick move, it was so incredibly tedious to traverse the burning battlefield. Then you have the golems with, insane crit rate. That shits stupid. And the insane mage with the infinite range spell. Half my team died, rip Bernie, linhardt, rip Sylvain. And also you can infinitely combat art rhea as edelgard what the fuck