I think your argument doesn't hold up all that well, you said that the improved architecture of the individual cores improved single-threaded performance (despite, I assume, the decreased clock rates), so I think Dr. Armstrongs point that the shift to multicore made sequential programming less profitable holds at least to an extent - if the CPU manufacturers used the same architecture but used just one core and the higher clocks th single-threaded apps would run still faster, but instead the multi-threaded apps benefit more from the improvements in the CPU.
The part of Armstrong's argument I was (explicitly) referring to was not about relative gains of multi-threading but about presumed absolute losses of single-thread performance. My argument against this is not refuted by relative gains of multi-threading..
Of course you realize even bigger gains on many common workloads using parallelism, but this part of his argument doesn't need the first part, which was wrong.
