1. How is the partner command/combat, is it too complicated, frustrating (especially the partner), or controls don't make sense?
Most of the time I just ended up using my abilities and trigerring some special attack with the companion.
2. It was definitely a bare bones "tutorial", but was it good enough to understand the gameplay? Or did you need more onboarding/more specific tutorials, if you even would be interested in learning more?
I think that the tutorial should make you hit or use the required abilities toward an enemy instead of just letting you pass by spamming the prompted button.
3. Did it feel like a unique system that you wanted to get better at and figure out, or did it feel like just a basic action game with a gimmick?
Imo I already have a lot to do with just controlling my character so I used the companion like a traditional fighting game companion (only special attacks from time to time). For now I think it is a basic action game with a gimmick because I don't feel that the companion fits a main role in the game design. I feel like it could be removed and the game would be the same, I expected it to have some advantage over some enemies or that it would help me kill enemies that otherwise I couln't.
4. And straight to the point with this, would you rather just have a entirely self-controlled AI for the partner instead of commanding them like this?
I think self controlled AI with the ocassional super attack triggered by the player is a nice middle ground.
It reminded me a lot to this game https://store.steampowered.com/app/2512450/SoulQuest. It uses a Devil May Cry style combo system, I think your game has a bigger potential for something like that with the enemy bouncing you can do with your companion.