My Asus router, when using OpenWrt, can't keep up with my internet connection, so I'm putting (admittedly minimal) effort into finding a suitable upgrade with the intent to keep the Asus as a backup.
I've also looked at installing OpenWRT on my USG, but only the snapshot version is available and the process is fairly involved[0] so I haven't really explored this.
At this point though, I'm not likely to go back to Unifi for routing. I needed to use the config.gateway.json (I think) workaround to add some DNS config[1] to my USG, whereas with OpenWrt I can do this entirely in the UI.
[0] https://openwrt.org/toh/ubiquiti/unifi_security_gateway_3p
[1] Just wildcard resolution so that *.internal.domain points to a reverse proxy server, nothing too extraordinary.