Well, look at it this way. If you just freeride, it will take time to become good at it. That means that skills must be learned, otherwise you'd be good right away. If you just do park, it will also take time to become good for the same reason. If they were the same skills for both, then having learned freeride for years I should be able to just step into the park and kill it. I've already proven that this isn't the case, believe me
. There's no logical reason to believe that it would be any easier in the other direction. Different skills, different reflexes.
Now mind you, if a park rat decided to take up freeriding, they'd catch on a lot faster than an all-around newb, but there'd still be a learning curve. Park snow tends to be sculpted and predictable (otherwise the park crew aren't doing their job) and in most parks you have very controlled and short approaches to things. If you stick to groomers when freeriding you probably won't feel too
different, but you'd be missing most of the fun. But it's the rough and 'natural' parts of the run that are the most fun. Those are also the parts that freeriders take longest to become good with, because
they're rough and natural, and the tossing about that you get takes some getting used to.