Some people improve by RPing with other writers, others don't. I know one dude who is a friend of mine and has been RPing for sixteen years who literally still writes at the same level. He's in it for the purest definition of casual fun. I, however, ended up writing alongside some talented folks throughout a similar amount of time and have only improved my vocabulary, use of language, and grammar. I have the drive to have fun [b][i]and[/i][/b] become a better, more interesting writer at the same time. Those are just two anecdotal examples. As for the criticism thing, yeah, probably. Most people kind of find it adverse and confront what they feel is unwarranted criticism with criticism of their own. No writer on this website is 100% objectively sound and without error.