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?
Your first part is what hurts me the most about both companions, tbh. The lack of scaling attributes just feels off to me. I get why they don’t, but doesn’t mean I have to like it. I’d love to see something like:
“At X level, your companion has been steadily growing in power alongside you. When you gain this level or whenever you summon a new companion, that companion gains a +2 to any ability score and a +1 to a different ability score.”