Right now I do not care about my wpm, it's at least as fast as I can think.
What I do care about is the ergonomics and the customizability, where the Ergodox Ez excels. I don't ever need to stretch out far or in any weird way anymore. Heck, most of the time I don't need to stretch out for my mouse anymore.
Huh, smaller could be better. I have huge hands but do not utlize a lot of keys on the Ez: I basically use home row and the big buttons in the thumb cluster ...
Now I've only used one split keyboard and only for about three years. The Ergodox Ez. And I think it combats every aspect you've pointed out, except the part about it being expensive.
However, put that into perspective and it feels like this keyboard will outlive me. I'll probably get another one for home use when I can go back to the office...