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A Themepark MMO with the Theme being PvP is a Sandbox.
Player made content is no longer a requirement, as long as the game gets no/very little PvE support,
and the main theme is PvP.
This seem to be the new age definiton of Sandbox MMO.
You dont even need to be able to change the world at all, as long as players know the PvE in the themepark is very lacking, and that PvP rules the game world, The general population wll see it as a Sandbox MMO.
things like FFA full loot only adds to the PvP theme of the Themepark. making it more of a Themepark with the theme being PvP.