Stay in Free then. Nobody will really judge you for the length of your posts there. Free seems to consist of one-liners and paragraphs at the most, so you may be more suited for that section. I'm sure that certain Arena, Tabletop, Nation and 1x1 Roleplays are the same as well. 

Personally, I'm horrible at describing and can still hash out at least three paragraphs if I need to. I also struggle to write posts due to my ADD (I can't sit still long enough to write posts sometimes), but despite the circumstances, if you're passionate enough about the subject, then you should be able to overcome anything that might stand between you and it. I should also note that post-by-post Roleplaying isn't for everyone and some prefer Roleplaying through chat, email and even videogames. It's possible that post Roleplaying isn't your preferred medium and you just haven't found it yet.

Regardless, I wish you good luck with your future Roleplay endeavors!