Offence is the Best Defence Achievement not popping

I am hoping this is a bug because I’m not keen on spending another several hours on this damn achievement

I decided to just have a crack at the achievement on my first go of the last Saladin mission, build a wonder and defend it from the 4 enemies, but destroy all enemies instead. Online strategy guides are few but it said to turn Persia to enemy and destroy them too, to get the achievement. First play through I realised I stuffed up and only set them to neutral so I played the whole scenario again- it’s not easy.

However the achievement still didn’t pop. Some people have said starting the wonder worked for them so I reloaded an auto save and tried that, still no Bueno.

Does anyone know where I’m going wrong here? The only things I haven’t tried are a) destroying Persia before they send their elephant reinforcements and b) not destroying Persia at all

I am at a loss but this being one of the hardest achievements in the game, I really bloody want it.

Does ANYONE have any idea how to make this work?!

Thanks folks