"America's Homer" isn't someone you pick by committee. The fact that you have to debate means that this person does not exist. The American literary tradition is far too new for someone to have the kind of impact as others on the list. We are talking about people who, through their writing, created and evolved language itself.
No single author has defined how America speaks and writes the way Dante did for Italian or Cervantes for Spanish. And perhaps no one ever will.