One part of what makes Orion such an attractive option to me on macOS is the fact that it's based on WebKit, which increases the diversity in browser engines. I also in general just prefer the GNOME design language - it's cleaner and more user friendly, and looks like it was designed by designers instead of developers.
On Linux I would use Epiphany, if it wasn't so damn slow and crashy. I'm kinda forced into using Firefox. But Firefox uses its own design language, so it doesn't really feel "at home" anywhere, and there's loads of tiny little visual bugs that add up to a million paper cuts. To work around this I use the Firefox GNOME theme because it looks so much better than Mozilla's skin. I would love to use a browser that really feels like it belongs on the platform it's on, like Orion on macOS.
(Slightly OT but if being platform-native is a goal then should QT's portability to Windows be a concern at all? I haven't seen a sleek native-feeling app for modern Windows built with QT, they tend to feel clunky and old)