Well, first, I think it's perfectly fine to have multiple takes on the same problem space. This is how we progress - people try different things, and we gradually figure out what works. Live-server does a specific set of things, and devd is a different take on a slightly wider set of things, and I think that's just dandy. The overlap is far from precise, and I think there's enough room for both devd and live-server (and for the many other tools that do similar things).

Second, not everything is node. Devd has lots of uses outside of node and even outside of front-end development.

Third, I probably wouldn't have written it if I didn't believe that devd did at least some things better than the current tools (at least for some people). You should try it - maybe you'll like it, and if you don't then that's fine too. As you say - to each their own. ;)