Totally understand them not being able to carry multiple people straight away. That can totally be the 15th level feature.
But at 7th level, it’s medium sized. Which, granted, is a wide spectrum. But surely it wouldn’t be too overpowered to allow the ranger conditonally permanent flight at that level, would it?
I think, instead of sprouting wings, they should get the capstone at the 14th(?) Class feature, and their capstone should be the ability to turn into a dragon.
Or at least bend dragons to their will, like Necromancer Wizards can with undead.