Re: the floating rails question; I think part of my original intent was also to ask why it seems fine for other games, particularly Adventure 2 and Heroes? It feels like there are more than a few levels there with a ton of free-floating grind rails that don't get the same criticism as far as I know.
In those games, the floating rails are there to provide flow in a specific direction. Like, it's not realistic, but it feels like they are leading you "forward."
A rail is a tool that helps you reach the end of the level. It is either leading you towards the end of the level, or away from it. And it's called a "rail." When people talk about games that are on rails, it's like, Star Fox or House of the Dead or whatever. Again, games that are directing you towards an ending. You can't "explore" when you're on a rail. You only have a destination.
Rails in Sonic Frontiers kind of do this, by their nature they all lead to a "destination," but they're crisscrossing all over the place and a lot of those destinations are strength or defense seeds, or caches of rings. Which are things that are basically everywhere, so having all these rails lead to them doesn't really mean much. So it's a lot of weird clutter.
Think of it like... Mario. In Mario you have pipes, bricks and coin blocks, right?
But if you think about the more open Mario games, like Super Mario 64, Sunshine, and Odyssey, you don't see as many of those things.
Because things like bricks, coin blocks, and pipes are tools designed to push Mario forward. Bricks can be smashed and don't come back, coin blocks can be emptied and become useless, and pipes take you somewhere. You can't really have these things in a big open area you're going to be revisiting multiple times, because their usefulness is limited and otherwise they just take up space.
And it's not just that a 3D Mario game cannot have these things.
It's a concept of linear versus open. The pacing of following a pathway and having tools or obstacles on that pathway. This is even part of Super Mario Odyssey, because there are routes that get more linear, as you ascend cliffs or buildings. And when that happens, you start seeing the return of coin blocks and things of that nature.
But never just floating out in the open. It's pacing, it's clarity, it's flow. And sometimes having a clear view of the sky is good for understanding scale and location.
Similarly, rails can still work in a game like Sonic Frontiers, but they need to be used in a more organic, targeted fashion. But a lot of that game's open world is a mess. You can tell Sonic Team had no idea what they were doing. No idea how to build or plan landmarks, no idea how to accurately direct the player on where they need to be going. A very nothing world.