Writing for Marvel is like playing in the NFL. They might take someone off the street, but almost everyone on their staff started at a smaller publisher and got their attention. You need to cut your teeth before you get called up to the majors. It’s not just your writing they need to question, it’s you ability to write any character and deliver on time, to hit the tone they want and write any kind of book.
The best way to get their attention is to write other books and do them well. Give them a comic to read, or better year write a comic that generates buzz. Smaller publishers are always looking for new talent and lots of the forum members have had success starting thatw ay.