but Setsuna's battle system was nice, they just needed to refine all systems that were kinda not really implemented well there, but potential is tremendous, and better balance..
What Setsuna really needed is more diverse locations, better characterization, better writing,
At least all negativism I've seen was about that, so IDK, to what fans they listened.
The game from what I've seen features a ton of diversity in locations (Victorian-era cities, fall themed forests, ancient ruins, waterscapes, etc) which seems loads better than snow and snow-only themed locations Setsuna had such as snow, snowfields, tundras, and ice caves. I consider that to be a major improvement already and they still haven't shown off much of the game or it's scope.
The battle system in Setsuna was nice but like you said they just needed to refine a lot of the systems. For me personally the biggest frustration was character placement since a lot of combos would rely on it but some characters had no real way of knowing where they would end up on the battle field. The ability to move -> attack fixes most of these issues although it has the unfortunate side-effect of slowing combat down somewhat since there is an extra "step". The combat here feels a lot more tactical because characters have different attack ranges (sword cyclone has a red circle with a variable radius based on your stats) that you want to try to encompass as many enemies as possible into. Other characters have guns that shoot in a straight line, so you want to position them in such a way that they can line up with as many enemies as possible. It's vastly improved, in my opinion. They're calling it ATB 2.0.
Another big fault of Setsuna is that the combat relied on too many random factors, I haven't seen any of those systems in Lost Sphear yet but that's probably also a good sign they've either gotten rid of them completely or that they're reworking them and don't have anything to show at this time.