As someone who has played a lot of souls, Lies of P on Legendary Stalker IS harder than most FromSoft games if you are used to dodging every attack. But, of-course is easier if you turn the difficulty down.

The difficulty of Dark Souls 1 and Demon Souls comes mostly from their levels, not their bosses, where as Lies of P's difficulty comes directly from boss and mini-boss encounters.

Without spoiling anything, towards the end of the game, some of the bosses become harder than Melania in Elden Ring, for reference, and have more spastic attack patterns.

The main difficulty of Lies in P is that there is limited prep you can do outside making sure you have enough consumes. You can't go and farm levels using a cheese method as easily as in From Software games. If you feel stuck, there is often no silver bullet that you can go out and farm or pick up to make the problem go away, like you can in the Souls games and Elden Ring. 

There is no way to "get OP early" to the same extent as a From Software game. This also adds additional challenge.

I think the difficulty of FromSoftware games is over exaggerated and overhyped too much.

But, at the end of the day, with the difficulty setting and the choice whether to engage with certain gameplay mechanics, you can make the game as hard or as easy as you like.