That may speak more to what you're doing with it. I've never needed extensive customization or extensions to do what I needed to do in REAPER, and I've been using it for many years (maybe since the beginning...I bought it very early on, and while I kept alternatives around for a few years, it rapidly rose to the top).
But, again, I use other tools for my MIDI sequencing and composition tasks. The MIDI and sequencing and loop-based composition side of REAPER is weak. But, the multitrack recording capability is quite strong, IMHO, and very easy to use. Maybe with extensions and going deep on scripting and such you can make it work well for those other tasks, and perhaps that's where our communication is breaking down. For me, REAPER is a super reliable, super fast and efficient, multitrack recording DAW that works exactly the way I expect a multitrack to work. I rarely need docs, I rarely need to fumble around looking for what I want to do.
I did note, in the distant past, that REAPER wasn't really competitive with Pro Tools for broadcast and film production work. While it had SMPTE sync, it was missing some other stuff...that I can't remember now. I guess R128 fits into that category of film/broadcast stuff that REAPER doesn't do well. It's cool that there's a set of extensions that covers some of that. But, by the time you're doing advanced stuff like that, it's always gonna require scaling a learning curve, right? I mean, Pro Tools isn't easy to use for advanced stuff (or for any stuff, really...I find Pro Tools somewhat unintuitive, when I haven't used it in a few years and sit down to poke at it again).
But, the comparison to vim or emacs only seems apt once you're doing hard things with it. I stand by my assertion that for the simple stuff, REAPER is very easy to use.
Thanks for bringing SMS to my attention! Looks cool.