Some parts of South America have a UV index twice that of Sydney’s maximum. All of the actually extreme UV index locales are extreme altitude and near equatorial.
Indeed looking at Oceania; Sydney, Perth, and Auckland all hit 14/15 regularly in the Summer months. Auckland in particular has ~40% more UV than comparable northern latitudes.
Given the genetics and immigration is heavily skewed in favour of the British and Irish diaspora, it's about 3x the UV Index of what the UK and Ireland see. Dunno where 10x came from.
The highest UV index I can find for Sydney is 14, which is typical of many places in the tropics.
I've spent time in the 20+ UV of the northern Atacama and it is a different beast. The indirect UV reflected by the soil is strong enough to burn you even if you are not exposed to direct sun. It requires precautions that I never needed in Australia or elsewhere in the tropics.