Anarchy costs 4. Serenity costs 2. They are both narrower and wider in different ways: anarchy can't even hit artifacts. Personally I'd rather have 2cc than 4cc, it makes a big freaking difference especially in legacy. And please do not use the cliche "doesn't get hit by counterbalance" argument, remember when that was rampant on the source? There was even a parody where somebody posted [SCD] Craw Wurm and one of the benefits was "High CC avoids counterbalance."
It's not valid. We don't bring in serenity for most counterbalance decks, and if we do, those decks usually board out counterbalance against goblins.
The metagame is changing and board-based control could reemerge. To judge so quickly is a mistake. Deck construction is much more complex than simply X and Y. It is not black and white for any metagame any of the 75.
I hate to say this but you really don't know what you're talking about.
Yes yes anarchy is pretty popular right now and has its benefits. But we are looking at this WAY too simply.

