The Asus TUF AX6000 uses the same SoC and WLAN chips as the GL-MT6000, yet they designed it with the USB port on the back of the router and there's no reports of any USB 3 interference. Yet there are some reports of USB 3 interference on the Flint 2, even with the USB port being on the side of the router.
An option to downgrade to USB 2 would be beneficial for the Flint 2, but other manufacturers have shown that it shouldn't be required.