I own and have extensively used both of these products. The Orbi may win in lab tests, and it is a brilliant performer when it works, but those don't mean much in the real world if it just doesn't work as it should and isn't reliable. The Orbi (RBK50) was the first mesh system I tried, took it back due to major stability issues, including regularly losing internet and satellites constantly losing sync. I probably reset it 30 times in the first day I owned it, it was that bad. Replaced it with an RBK43 system which was not a whole lot better, and ended up calling support. Turned out I even had to leave the default SSID in place for it to remain somewhat stable, and even that didn't stave off the satellite drops for long. I tried an RBR50 router with two RBS40 and an RBW30 satellite, same issues. I still have several pieces of Orbis i don't use.
I do agree that the Orbi has a better 5 GHz client connection, but the Multy seems to have a more stable backhaul connection as my satellite has never dropped after weeks of ownership. The computers I use most often are connected to the satellite via ethernet and I get my my full paid internet speeds all the time and a 400-450 mb/s backhaul connection.
I now use the Multy X system, and while it is far from perfect, it is leaps and bounds better than the Orbi from a stability standpoint. I did have some issues with Multy (turned out to be Google Chromecast issues) and reached out to their support, and the problems appear to be resolved as Google released a fix. It's also easier to control/reboot remotely via the app when I am traveling, and (unlike the Orbi) I have never not been able to access my Multy through the app while on the road. You can also reboot the Multy satellite independently. Real-world performance feel and speed test numbers in my small house are very close between the two systems, and both easily max out my 300 down/30 up Mb/s internet connection. The Multy units are also interchangeable, unlike Orbi, and each Multy can be used as a router or satellite. I will say that while the Multy's app works very well for setup, it's pretty horrible for all but the most basic functions, and Orbi is much more configurable with its web page, if you can get the config to work right. All in all, I'd take the Multy X any day over Orbi.