I don't believe he modern series (Post Mana Khemia) is particularly focused on innovating on what it did before. Instead, it tends to experiment with different ideas while keeping the core intact. That's how you get a JRPG otome game that turns into a kingdom management game by the final entry or a subseries with semi-open world exploration with time management followed by Lydie & Suelle world-hopping approach. Lately, though, they've been playing it much safer because they don't seem willing to move away from the semi open world formula. So you could argue that Ryza 1 through 3 did show some evolution, albeit a fairly small one like you mentioned, because Gust was playing it safe, very safe. In the end is a series for JRPG autists that like to grind more than XP, but also resources, and I think Gust is satisfied as long as they can fulfill that basic requirement.