Tbh SimpleX is even worse regarding moderation. All these very private messengers are just bad for moderating big rooms.
As these rooms are public, treat them as public. It sucks that you need to split tunnel Discord, I experienced the same and even after adding a real phone number I couldnt join a chat, just because of a VPN.
But in the end, use SimpleX or XMPP where you are in control, but these are not suited for public rooms.
Tbh I would also only use Matrix for public rooms, it isnt really privacy friendly either.