What I have observed with Arch is it's slow increase in popularity, which also seems to be it's demise. Arch went from 30 or 40 something on distrowatch and now sits on 9th place. Still increasing in popularity! I'm getting a feeling that it might eventually overtake Debian and Mandriva. Back when it was in the low 30 ranks, x64 binaries were a dream come true and it was the only sensible i686 based binary distro. (personal bias) Now though, there are many x64 binary distributions available and arch is starting to loose it's appeal. Not to mention it also seems to be more problematic lately.
Arch just rules. I use it for over one year now and I had no serious problems. Yeah I was a distro-hopper previously, but now distros are distros and Arch is Arch.
Your claim guys is amateurish, the power of Arch stands in simplicity and customization, it works way faster than Ubuntu overall, not in batch tests which have nothing to do with the distribution, but rather the kernel, filesystem, compile flags and so on. Optimizing Arch is just a matter of editing the compile flags in /etc/makepkg.conf and rebuild the packages which matter with the descriptions in /var/abs - that's it! :)
My girlfriend is on Arch + a heavy customized GNOME and I can confess: her installation is noticeable slower than mine - possibly even slower than a default Ubuntu installation - although I didn't touch this distro for some years - I'm on XFCE, but she said that she will move over XFCE soon (after some exams). So this is the issue, one has to know what - and sometimes how - to install in the system. Linux is Linux and the dumbest distribution can lead in such tests - because the Kernel does its job - anyway.