It gets tougher towards the end

In the latter half, hero rarity and resource management must be meticulously handled, hmph! Making them 4-star at level 10 to boost skill efficiency will be a wise strategy, y'know. I hope you'll patiently build up your foundation with a benevolent heart, hmm!

That's how all games are. They're super easy at first, and then the difficulty gradually spikes as you progress.