The difficulty of the game is unclear

Started playing the game + after my brother on only the second difficulty and the enemies fell me with 1-2 hits, but I'm their currency with a couple of kicks. Yesterday I had an encounter with the first boss - one-armed gray-haired jidai and he rolled me with one punch. Started the second round, I rolled him with one punch, charging a punch in the block! Changed the difficulty - the same thing! Is the game broken or what?