I think one thing that has not been brought up is the Remans have Thaleron weapons tech. That tech could kill any organic creature in the blast wave. So that might be used against the Worldship by the Romulans.
The Vulcans know how to make it.
As to the Worldship.
The Doud, The Organian's, Trelane's Race and The Q take one look at it and say "Get your Buster Ass out of here!!!" The Star Trek Milky Way has too many god tier beings for them to be successful.