Any question answered...

^I tried that, sanded the edges real carefully and used a tiny bit of filler to get it completely flat but it's still visible and looks shit. I used to be a plasterer, which oddly enough meant there was no way I could be arsed to skim it.

Either scrape all the paint off (PITA) or get the ceiling skimmed.

That polycell flexible cieling stuff covers a multitude of sins