Wholeheartedly agree on having more platforming. Those are some of the best parts and challenges of the game.
When it comes to the battle system, I'm not talking about being able to select attacks or control Sable (other than being able to escape), but rather, add effects that could happen during the course of battle to give it more variety. Maybe enemies could induce a couple of different status effects whose effectiveness varies depending on the transformation. If you're facing a venomous scorpion or spider that can poison, then Sable would want to transform into a snake or a creature with a thick hide where the venom wouldn't have any effect. Perhaps the terrain you fight on can impact the tide of battle too. It's really little details like those that enhance how you have to make pre-battle calculations such as if you have enough power or if you're in the right transformation. I really like that feature and it'd be about adding to the strategy, not the mechanic of fighting itself.
I have to agree with you on the party members, though. Maybe they could enhance Sable's stats in some way rather than be full-fledged members so he can still fight while they're around. They don't have to be permanent either, but it gives me a reason to see Richard more, lol.