is the ending effective?

I think it is. The three pairs of lovers represent the comic ending. But what should be a happy ending is violated and broken by Antonio and Shylock. Both men remain outsiders at the end of the play, alone and removed from the happy luxury of Belmont. Both outsiders also have been immasculated by the end. Shylock via the loss of his money and his daughter, Antonio by losing Bassanio to Portia. The lowest level of Antonio's defeat is when Portia hands him his money and ships at the end, essentially telling him to return to Venice and forget about Bassanio.