I presume you're talking about the link that Frankie posted, not Muspellsheimr.
In that post, AH first defends the FAQ ruling on splitting dice pools: "A dice pool is generally Skill (+ Specialization) + Attribute + anything else that adds directly to the dice pool but is not listed as a dice pool modifier (foci, certain augmentations, etc.)." However, weapon foci are explicitly listed as dice pool modifiers! "When used in physical combat, weapon foci grant the character a dice pool modifier to melee attacks equal to their Force" (SR4A, p. 199). Furthermore, the FAQ ruling makes no sense when applied to two-weapon fighting. It's because of things like this that I don't trust FAQs when they contradict the RAW.
He does call the mystic ruling the "closest the FAQ comes to an actual errata, meant to reflect the actual intention of SR4A." But then the justification given is that it avoids abuse of the character concept. I'm wondering just where the abuse is? My impression is that most people think mystics suck balance-wise. Our group's big power-gamer thinks they suck even with the generous ruling. Frankly, I think you need to be generous with the magical power just to play them successfully as described, or they have the same problems that multi-classed spellcasters had in D&D3. The generous ruling doesn't allow abuse, it allows playability.
So given that half of that post is outright wrong, and the other have has shaky justification, I take it with a big grain of salt. If they mean to change the rule, they really should subject it to a higher level of scrutiny. I think far too many people (including the designers) have a knee-jerk reaction that it's over-powered. However, when you compare it to what an ordinary magician can do, it really isn't a big deal at all.