On the scales that youre talking about  fewer than a hundred unique sites put together  vs   a ratio of  not  both forms are so rare as to make such comparisons almost irrelevant For this hypothetical reader who wouldnt be able to figure out what ecumenopoleis means from the context it is given as a plural form at the beginning of the article It is patronising in the extreme to assume that using the etymologically correct plural will cause such difficulties  particularly as all readers need do if they are confused is open the ecumenopoleis article in a new tab  window to be told what it means in the first sentence The last remaining argument is sthetic  it is undeniable that a  ending sounds a lot better and is far easier to say than a  ending