Too early in the game for me to say and I've only played Bloodborne, albeit I platinumed it with no summons. I will say that my experience so far has been a bit like Bloodborne, almost feels like overwhelming difficulty at first and you feel so vulnerable, but after a few bosses something clicks and it starts to get more manageable.
But I lean towards Sekiro being a bit more difficult. I am at Ashina Castle and I've gone off in some of the alternate paths and seen enemies that I am clearly not ready for and can't imagine beating at the moment. Bloodborne clicked for me and I leveled to the point where I got several bosses on the first attempt, only getting stuck on a boss or situation every now and then.
So far with Sekiro I don't think I've reached a boss or miniboss yet where I haven't been stuck for at least a little while. Although I think I'm slow to learn that most everything can be parried. Like I didn't think the Horseman or the Bull could be parried the first time I played them, it seemed silly to think my sword could do that. But then when I discovered you can, those fights became much easier.
On the minibosses I think I just need to study their movesets more closely; those frequently being surrounded by grunts is probably the most troubling thing so far in terms of difficulty for me.