Yeah, Decidueye joins a list of Pokemon who look like they should be immune to Ground-type attacks but aren't. You COULD justify it, if you notice Decidueye folds its hands under its shoulder and to fly it looks like it'll need to have them spread out, so you could take that as Decidueye giving up its flying Ability to focus on being stealthy and its archery. It's weak but its the only justification I can see, at least its better than Beedrill or Volcarona who is seen flying in the air but still take Ground-type damage (and if it wasn't for their Bug-type they would take super effective damage from it).
I do agree they do need to make a Magnet Rise for winged Pokemon who aren't Electric or Steel. I always thought it would be called something like "Flutter".
I'm on board, if for no other reason than me wanting to see the text "Ribombee used Flutter!" Too cute, too cute.
So, the datamine has revealed something interesting. So, apparently the in-game check for whether you have a Z-Ring or not refers to it as the Zenryoku Ring, meaning we know know what the Z in Z-Ring means. For all those curious "zenryoku" is Japanese for "full force", making Z-Moves "Full Force Moves", which is quite fitting.
Also, to chime in on the game having a check in place for whether or not you have a Mega Ring, aka this:
- I'm a bit skeptical of this one. We know they left in all the Mega Items in the code so just because there's a Mega Ring doesn't mean it'll be used. Also didn't we see the player using the Z-Ring to Mega Evolve?
My best guess is that they use the "Mega Ring" check to check whether or not your Z-Ring has a Key Stone in it, but they just decided to keep the in-code text untouched, since it wouldn't matter what was hidden beneath the surface in terms of gameplay.