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?
Playing a drakewarden character sometimes feels like finding narrative explanations for undesirable mechanics. Although, whether or not the drake companion works as a flying mount is dependent on the campaign. Seriously, rules lawyer-ing the dragon mid-game sucks.
A narrative explanation might simply be the drake doesn’t know how to fly properly with a rider at medium size…
To make it a non-issue, I chose a variant Tiefling, winged, so my PC can raise/train the dragon from a hatchling and fly with, rather than on.
Regardless, versus other class options, the drake is still a formidable familiar, and rangers don’t normally get an option to just fly at will (without a magic item) anyway.
Besides, half the reason for choosing a class is flavor. They don’t all have to be able to do the same shit at the same level.