I could be crazy, but don't all the external antennas allow for more flexibility with regard to directionality of signal?

I have a U7 Lite and it is very directional compared to other routers I have used (spider style, trash can style, etc.)

The U7 Lite only does 2x2 MIMO. Compared to 4x4 MIMO in the U6 LR, the U7 Lite therefore does a much poorer job at beamforming (directing the energy of the signal towards the device).

Personally, I find it better to have multiple low end access points (like the TP-Link Archer C80 which has 3x3 MIMO on 5 GHz) deployed to achieve excellent coverage in a house. Sadly, the U7 line is a bit too expensive for that. Plus, I'm loathe to deal with UniFi deployments now that I am well versed in the glass jaws in the platform.

There really is space in the market for a product line that is basically what UniFi is, but done "right". Ie: can be debugged or you can fix it without an internet connection or recover the system when the owner forgets the password and lost access to the email account used for 2FA. UniFi is an absolute nightmare the moment anything goes even slightly wrong.

Yes, perhaps they do allow for greater flexibility, but that's complex and difficult to do well/reliably, and doing it well/reliably requires signal analysis gear and software modeling that's out of the reach of normal consumers.