Yeah, ringing the demon bell just makes enemies hit harder and have more health. There’s a second way to increase the difficulty, but you only have access to it after you’ve beaten the game. It beefs up enemies, but also makes it so you take chip damage when guarding, meaning you have to parry to avoid damage altogether. The second method makes the game harder in a good way
I’m surprised you even found the second owl fight on your first run. The Demon of Hatred is a tough one for sure, but people say he’s the most dark soulsy boss in the game. It wasn’t obvious to me, but there’s actually a way to reliably avoid his charge, and it doesn’t involve dodging.
A really tough boss is the spear wielder with his sword pal at the Ashina Reservoir idol during the third act of the game. Fighting them 2v1 is a true test of skill.
A few of my friends and I were really into the game, and we had a blast streaming our playthroughs and watching each other. The only one of us who didn’t think much of the game also didn’t consider it much of a challenge, though he extensively used Shinobi prosthetics, mortal draw, consumables, and even guides. I can imagine how the game might not live up to its reputation if you’re able to just plow through it and not feel the sense of accomplishment that can only come from finally beating each boss after they’ve stomped you into the ground a dozen times.
I hope you enjoy the last boss and it makes the game seem worth it, or maybe you give it another go using one of the items that cranks up the difficulty, and you find some joy in that. I just think it’s a special game, and I want everyone to love it as much as I do.