(A) As it has been for several decades, Disneyworld being the top tourist destination in America last year, welcoming more than 3.8 million visitors
no need to make it passive and redundant
(B) As it has for several decades, Disneyworld was the top tourist destination in America last year, welcomed more than 3.8 million visitors
welcomed awkwardly modifies last year
© Disneyworld, as it was for several decades, being the top tourist destination in America last year, welcoming more than 3.8 million visitors
(D) Welcoming more than 3.8 million visitors, as it has been for several decades, Disneyworld was the top tourist destination in America last year
two modifiers next to each other is not advisable
(E) As it has been for several decades, Disneyworld was the top tourist destination in America last year, welcoming more than 3.8 million visitors
welcoming correctly modifies disney world
HTH