When Danzo fought Sasuke he used Izanagi with only sharingan's i suppose it was thanks to Hashirama's cells but what about Itachi, Madara,Obito and the ancient Uchiha clan?
You're probably confused by the garbage filler episode in which apparently everyone and their grandma had MS, and only those with MS happened to use Izanagi and Izanami. But filler is filler, and canonically all that is needed is the Sharingan for an imperfect version, and the Sharingan and Senju dna for a perfect version.