This being on Tor gives me mixed feelings.
Tor's a volunteer run, fairly resource-heavy privacy tool designed to protect the most vulnerable internet users out there -- people facing state censorship on the level of corporal punishment being used, for example. While the Tor network has more capacity these days than it used to, and while having a good toolchain for Tor's intended user base matters, that's rarely the intended user base of apps like this.
When something like Quiet comes along, even with its targeting of users in open societies, it would benefit both technically and ethically from using non-Tor networks: HTTPS is safer than ever, and if you use ECH, DNS-over-HTTPS, and have reasonable cipher requirements for TLS, you can achieve an excellent level of privacy.
For when open society groups need to talk to people at risk of harm, having a Tor bridge or other such mode would be a good way to approach that. It also makes implementing video and audio much easier technically, and it decouples the "casual user" code base from the "sensitive user" code base; while that means you might have less shared code, it also means you can focus on security through simplicity (by way of fewer or less-complex features) for the sensitive users.
[0] https://news.ycombinator.com/item?id=37480552