A friend! :)

The moment I realised that the chat mix could only be managed via software (even though a hardware controller is still available), I packed up and returned it.

The Arctis 9 (the old version, not 9X) offered everything I wanted and was below the RRP of the Arctis 7 at the time (only available second-hand here). But when this one gives up the ghost, it's going to take a lot to keep me buying models from this range.

I'd also like to know about products from other manufacturers with multiple audio endpoints and hardware controls.

The same here. I'm not a fan of it either. I got myself a Stream Deck and with it I can easily turn up and down every single programme as I like. With the Discord plugin, even the individual users can do it easily. Maybe worth considering for you. So you can use any headset you like. What doesn't work is if you use the ingame chat.