The changes introduced in Cataclysm increased the difficulty of playing Warlocks to the point where players who previously were proficient were no longer able to keep up when performing under duress. Raising the bar of competence doesn’t suddenly make someone a “baddie” if they fail to keep up.
Honestly, if they could play Destro WELL in Wrath, but can't play Affliction, that's a l2play issue, not a class issue. Affliction has its own problems, but complexity is not one of them (outside of min/maxing multi-dotting, which is absolutely unnecessary in any context in which complexity is an issue).
Don't compare Wrath Destro to Cata Destro, one was THE easy spec and the other is, IMO, THE "hard" spec. Compare Wrath Destro to Cata Affliction:
Immolate: that you must time to end the cast as the dot ticks off. If you clip it, you get punished, HARD.
2 short CD's
Movement spells: Life Tap > Corruption
Corruption (easier to maintain than Elements in Wrath)
UA: you have about a 2 second window to time the cast perfectly, or you can cast it late and lose some uptime. The latter issue was the same in Wrath, but if you cast it "too early" you're not going to lose 3 seconds worth of uptime for your mistake.
2 short CD's
1 two-minute DPS CD (I wouldn't suggest it, but casuals could macro this to Doom or UA)
The only thing that makes Cata Affliction any more difficult to learn than Wrath Destro is the number of buttons. Otherwise, I'd actually say it's easier to play, you don't need to deal with clipping LT uptime, you don't have to deal with clipping dots, you have far more room for refreshing your dots without "error". The execute is laughably simple.
You can't literally roll your face on the keyboard, like you could Destro, and still put up numbers. But, anyone that bothers to even look at their game screens should be able to play Cata Affliction, albeit some people may resort to clicking CD's or whatnot that they wouldn't need to do with 6 button Destro.
The depiction of Cata Affliction in the article is entirely off base. For the most part, you don't need to watch Shadow Embrace, even in heroic content there's only a few encounters where it's an issue. For the most part, DI is just static noise. Drain Life? WHAT?! Fel Flame has the same significance as Wrath Destro's Corruption, you use it when you have LITERALLY nothing else to do while moving.
“I have 3 adds don’t let Shadow Embrace fall off of any of them.”
This might be tougher to tackle than "Keep up Immo, Corr, and Doom on one target, Immo, Corr, and Agony on another, Conflag on CD, Shadowflame on CD for the cleave, and make sure ISF is always up when applying dots", but neither of those are necessary in the context in which they're presented.
Also, this is 4.3 already. This isn't 4.0.3 anymore. A lot of what was discussed was fixed pretty shortly after Cata's release and I don't think it's really relevant to the problem. I certainly do think Warlocks have many issues, some of which it seems they're working on, but, as much as I appreciate the thought that went into those articles, I just don't agree witht them as much as I did the others.
Edit: Simplexity addressed a lot of the points I was aiming to address while I was typing.