Absolutely not. I rode the 2012 Evo 153 when I was around 150 lbs (how much do you weigh?). While it is not ridiculuously noodlely like a Ride Kink or Burton Dominant ... it is still a pretty soft board, especially compared to something like the Custom X (what length were you riding?). I'm not familiar with the Postermania, but according to the Rome website... that isn't a jib board either.
With your experience and background, I think it is a lot more to do with rust and the fact that you might not have found the sweet spots on the flex for the Evo 150 yet.
Another thought: it kind of sound like while you are an experience freerider... you are relatively new to jibbing (i.e. started it last year). Is that true?
I weigh 140 to 145. The custom X was a 152. On paper, the postermania doesn't look like a jib board but I found it softer than my friend's WWW.
It definitely could have been some rust and not being used to the board. I only got about 7 or 8 runs in this morning. I've never ridden an RC board either. The postermania is rocker/flat and it didn't take more than a few runs for me to 'feel the board' if you can understand what I'm trying to say.
Yup what you're saying is true. The majority of my snowboarding experience is freeriding. I started to mellow out two maybe three seasons ago. Last season was when I started to spend more than 50% of my time in the park. I plateaued for a while when freeriding and now focusing in the park has made snowboarding fun all over again in a new way.