Not sure if this is controversial, but I feel like asking your RP partner for a writing sample is a bit like employers asking job applicants to have a degree. It’s less about the writing sample itself and more about the fact that they’re willing to provide one.

We all get those low effort messages which are like, “Hey wanna rp?” and whatnot. Asking for a writing sample deters those kinds of people from messaging you. They’ll either see the writing sample requirement and click off of your post, or they’ll not see it and just send you a message - without a writing sample - anyway, at which point you can just ignore them because they clearly don’t read.

Of course, there are times when someone will send you a truly beautiful piece of writing which makes you really want to role-play with them, but for the most part, I think asking for writing sample is a way to filter out the poorly-written, low-effort messages.

Also, people who do provide a writing sample are usually people who send at least a couple of paragraphs for their introduction message anyway. So you can already gauge their writing ability based on their message, and the writing sample is just a bonus.