I think it also depends on the system you’re using it on. I think one of the biggest advantages of DDB is that is scales so well (with good design to avoid hot partitions). Afaik, RDBMS simply cannot scale in the same way due to their design. Yes, they can scale somewhat, but as you said it requires lots of tuning, and you’ll still reach a hardish limit.
I think it’s more like cross-world latency. Where going from one side of the world to the other will be slower going via fibre optic vs through space as with starlink? I think this is reliant on the satellite-satellite latency being low and the ground to satellite being not insanely high.
A switch exists for this, however they’re quite expensive and had some financial issues in the past (although they seem to be under new management now)? https://dendevices.com/products/switch/
If your server has full disk encryption it should be relatively safe against attacks where they just take the device, and so whatever you use to sync should be safe too?