Umbrella is a legitimate cheese strategy to almost any problem in the game, I think of it as a crutch to help players get through some tough spots where they would otherwise give up. In my case it was the Shichiman warrior on the first playthrough, I could not fathom facing him without my purple umbrella (I was weak
). It can be used to cheese the super fast samurai, the centipede warrior thing and so on. It even cancels Chained Ogre grab attacks
I'd say use it in case of desperation, but just know that it is never essential. Snake Eyes's musket can be sidestepped for example . The crow feathers prosthetic is a similarly powerful crutch.