Those 'actual amateurs' have budgets and facilities and salaries that equal and sometimes top the Eerste Divisie teams. So really a lot like League One and Two in England.You think cup upsets don't happen here? Top flight teams are knocked out by actual amateurs on a yearly basis.
But either way the point stands. Lower-league clubs manage cup surprises in the Netherlands as well. The FA Cup isn't quite as unique as people from England seem to think.