Some educators believe we learn first to read and understand language even if it is only looking at pictures. This is input. Once we understand the reading world, we graduate to writing, which is the output.
Of course, this could be wrong. Some educators believe we learn to write before reading (look up Maria Montessori). These educators see children drawing pictures as if writing their own language while acting out stories before learning to read.
It’s not necessary to get into this debate (particularly since I’m not an educator). The important part is that a writer should read.
There are some writers who do not read, yet they find readers for their work. For these few writers, it seems to work. For the majority, it does not. I’ve read work from writers who proudly announce they do not read and their writing is difficult to understand. I sometimes wonder if it is even English.
I believe reading is an important way for writers to understand what they are writing. It is a way to learn. Whether a person sees reading as input and writing as output or the reverse does not matter. They are both linked and woven together. Writers will struggle when they do not read.