Hey everyone,
Thought I would chime in since I just did this upgrade. From my experience, I can agree with the blanket statement quoted in the OP's posting. But that's just my experience, so far, FWIW.
My system is rigged with 100% Anti-Cables for Speakers, ICs and Power Cords. Since I have WAF considerations, my speaker cable lengths are absurd: 33ft and 40ft (I know, that's like an audiophile horror movie). With those lengths, I can submit that in my very revealing system, supremely pure solid core copper wires definitely trump stranded cables of similar size and length.
I had been running the original anti-Cable Speaker Cables for many years and they sounded so sweet. But I just installed Paul's Level 3 cables, which are now directional, higher purity and beautifully woven. The difference, ROOTB (right out of the box), is not at all subtle. What the level 3 cables have shown me already, is that especially for long runs, going to 9 gauge of solid core is definitely an upgrade that's easy to justify.
Paul just came out with solid silver phono cables, which I heard at a friend's place... Nice!
Side note: I'm trying to get some forum traction for this acronym ROOTB since I write it often. If you do as well, please pass it on.