I think, generally, the Orbi is good at getting good speeds to multiple devices over a large area, even via the satellite. I think it is less good at getting maximum speed to a single device. But, accoring to this review at Tom's, ~550 Mbps is the peak performance for a single device (though you might find that you can approach that with two devices, simultaneously, using the Orbi). When you did the speedtest on the ISP-provided router, were you using wifi, or was this over a wired ethernet connection? Also, are you testing on the same device (e.g., laptop, phone) for both tests? Depending on the age and size of the device(s), there may be more or fewer antennas, and different standards (your laptop could be 803.11ac, whereas your phone might only be 803.11n), either or both of which could affect speedtest results.
You might also find reading on wifi, generally, and 802.11ac helpful.
