>In fact, some compression modes would actually slow things down as my energy-efficient NAS is running on some slower Arm cores

Depending on the number/type of devices in the setup and usage patterns, it can be effective sometimes to have a single more powerful router and then use it directly as a hop for security or compression (or both) to a set of lower power devices. Like, I know it's not E2EE the same way to send unencrypted data to one OPNsense router, Wireguard (or Nebula or whatever tunnel you prefer) to another over the internet, and then from there to a NAS. But if the NAS is in the same physically secure rack directly attached by hardline to the router (or via isolated switch), I don't think in practice it's significantly enough less secure at the private service level to matter. If the router is a pretty important lynchpin anyone, it can be favorable to lean more heavily on that so one can go cheaper and lower power elsewhere. Not that more efficiency, hardware acceleration etc are at all bad, and conversely sometimes might make sense to have a powerful NAS/other servers and a low power router, but there are good degrees of freedom there. Handier then ever in the current crazy times where sometimes hardware that was formerly easily and cheaply available is now a king's ransom or gone and one has to improvise.

  rsync -e "ssh -o Compression=no" ...

You'd be astonished at how much faster even seemingly fast local IO can go when you unblock the IO