fyi, there are two ways of using X across the network. The X forwarding via an ssh tunnel that you refer to, is technically rendered on your machine where you forward the DISPLAY from. The X client on the remote side is a 'client' and connects to your forwarded (local) display. The rendering happens in that display server (local) that dumps the result into your graphics device framebuffer/onto your screen. The instructions though come from your client on that remote machine, incl. any drawing primitives like drawing a line etc. But still the actual resources that client uses are local to your X server.
The other approach is (and that was like in the older days), when you avoid any tunneling but let X clients connect to open X servers across the network, like if your X display server listens on all NICs for clients. This setup is still technically possible but pretty much discouraged for security concerns. But with this setup you could also run a local xterm or whatever X client against a remote X server (like your neighbours ;), assumed it would accept your connection.
As pointed out above, suckless isn't focussing on macOS/XQuartz users. The latency of "linux-st" isn't that bad according to the plots of the author.
In my view, simplicity often leads to better performance as a side effect -- but of course there are many exceptions.
Nevertheless, I wouldn't start optimising software unless the software is really unusable. Optimising software to look well in rare corner cases is not a good idea imho, if the price is adding a lot of complexity.
Suckless isn't focussing on macOS, as Apple software clearly isn't targeting expert users, but rather the mass market of noob users.
If you double check the plots, you will notice that "linux-st" isn't performing bad at all. The author also suspects XQuartz as one reason for the higher latency, which makes absolutely sense.
The other approach is (and that was like in the older days), when you avoid any tunneling but let X clients connect to open X servers across the network, like if your X display server listens on all NICs for clients. This setup is still technically possible but pretty much discouraged for security concerns. But with this setup you could also run a local xterm or whatever X client against a remote X server (like your neighbours ;), assumed it would accept your connection.
Like: DISPLAY=yourneighbour.host:0 xterm
BR, garbeam