We can fully see how the uchiha are so OP from madara,sasuke ,tobi,itachi and shsui .They all advance from basic sharingan (tobi stiill unknown).
The reason why Danzo knew that if the uchiha clan sharingan get advance beyond basic sharingan then it will be an unbalance in power in konoha.The uchiha clan will be hard to control .So he prevented people from advancing to MS and rinnegan because he saw how OP madara was during past shinobi wars
The reason why Danzo knew that if the uchiha clan sharingan get advance beyond basic sharingan then it will be an unbalance in power in konoha.The uchiha clan will be hard to control .So he prevented people from advancing to MS and rinnegan because he saw how OP madara was during past shinobi wars