Roleplaying in an MMO is most certainly a different beast than roleplaying on a forum or via an instant messenger program, so not liking the one while enjoying the others is totally understandable. 

I've done a fair amount of in-game roleplaying, mostly in World of Warcraft back when I played it, and honestly I can't stand the usual RP fare you find in such a game. The people just hanging out at bars and chatting is just tedious. I would probably be in your same situation of disliking in-game RP if not for the fact that early on I found a couple others who felt the same way, and those people introduced me to others, so I found my way into a group of roleplayers that disdained the normal in-game stuff.

We roleplayed like we were on an instant messenger program, with full descriptive stuff despite it all being technically done for us by the game. Most of us got a mod for the game that allowed us to ignore the character limit for posts in the chat system, so we were able to go long with it whenever we wanted without any issues. Sometimes we'd RP over IM programs and it was basically the same experience minus the need of having to find a good outfit or a nice place in the game to RP.

Anyway, I'd suggest you try one of two things. First, maybe try to find your own group of people who shirk the norm for MMO roleplaying. There are bound to be other people out there who like roleplaying but aren't keen on the quick and short responses game, so all you have to do is find them. Or, if that doesn't seem like a viable route to you, go ahead with what you already said and find others who share your preferences. Trying to force yourself to roleplay in a format you're not comfortable with will just be a pain in the ass and a lot of time spent feeling awkward instead of having fun, and there's nothing to be gained from that.