About Decadency Revolt army size
After falling into full decadency my Shia Arabian Empire (consisted at this point from Egypt, Siria, Arabia, Abyssinia, Perisa, Khiva) was attacked in eastern parts of Arabia by 500k army. All i could scrap was 150k.
Maybe number of enemy troops somehow connected to time passed after reaching 100% decadency? In my case it was probably 10 years.