I mean don't get me wrong, I'd love if using a hex grid was an option as well, but I think Olive had good reasons not to make it so. I'm by no means fluent in coding of any kind, but it does make sense to me that trying to code for hexagonal LOS and movement (especially for Size 2's, where their asymmetrical shape could cause problems, especially if trying to implement being able to "rotate" them so that their triangular area flips directions, which I typically see ruled as moving 1 space) would be far more difficult than just coding for a square grid. If it isn't feasible, it simply isn't feasible.
I don't think the circular method whilst using a square grid is all too great of a solution either. The simplest would probably just be the "boxcar" method, where you can't move directly on diagonals, and instead must make two cardinal movements (one up, then one left, for example), but that has its own disadvantages in making diagonals unrealistically short. You could even do a thing I've seen in some D&D games, where every other diagonal costs one extra space of movement, to make it adhere closer to 45° measurements, but that also seems like it would be annoying to code and make work with everything in the game.
Realistically I think it's not too bad just getting used to the square grid. I come from a D&D background so I'm familiar with it already, more so than hexes even, but I understand that's not the case for everyone. The main thing, in my opinion, is just making the game work, and being able to make it in a timely manner that avoids unnecessary fuss. Opting to use squares instead of hexes seems to be by far the more economical choice for these reasons, and I can't really fault Olive or the other team members for going with that. It's a passion project, no doubt about that, just look at all the care taken to render the game as faithfully as possible - it almost puts Athena's Simulacra to shame. But there's always a line to be drawn between suffering for the sake of passion, and suffering beyond reason. I've heard enough horror stories about trying to code different games or programs to understand that said line had to be drawn somewhere, and I think it's in a good place as it is.