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?
My greatest problem with Drakewarden is that you do not get additional dragon themed spells and that it takes forever to get a flying mount. If WotC is okay with Twilight Cleric and Genie Warlock getting to fly so damn early on, I see no reason why Drakewardens cannot fly at like level 7 or 11.