I think why it works better for me in Sekiro than in Elden Ring is that Sekiro has both a more interesting progression (you unlock new tools and techniques more than just higher numbers), as well as a stronger narrative through-line. The bosses also feel more like puzzles rather than different shaped attacks to dodge. Not to slight ER or say I don't like it, but there is a reason why I like Sekiro more.
The mini bosses feel more like just a stronger type of enemy rather than the dungeon endpoints like they are in ER, and the arena you fight them in is much more relevant too. The two centipede fights for instance feel very different, as you approach one from a very advantageous position, but it is surrounded by allies, and the other you are just locked in a small room with it. And all the drunkard fights have very different setups that pose their own challenges.
There is also some good storytelling in the boss repetition, fighting Genichiro three times tells a great story, and then seeing his style echoed in the okami warriors reads more world building than repetition.