Csar: We fought, and won, and celebrated the day that we rested from our enemies. You can try and splice the resting from the winning, but it’s clear that we celebrated winning a battle in which we were fighting for our lives.
And I am not familiar with that Meshech Chochmah, but I find it hard to believe that he says as you quote. Because the Gemara itself gives Ester’s answer. Her answer wasn’t that it was the resting they were celebrating, it was that the Goyim already know (“they are written in the histories of Persia”). So either he’s giving a different answer than the Gemara does or you’re misquoting him.