Now try a melee run!
In terms of difficulty running melee builds I'd probably rank them from most difficult to easiest on first run:
Bloodborne DLC > Demon's > DS2 (including DLC which was pretty challenging) > Bloodborne > DS1 > DS3
I thought going back to Demon's, having cleared all the rest and been done with Souls git gud would've made Demon's a breeze. And maybe it would have if I ran a mage build since like 90% of enemies/bosses are only melee range on their attacks, but running melee, I thought Demon's was still hard as fuck.
Though in Demon's its the levels, not the bosses, that are the difficulty. Bosses are only Flamelurker/Allant and Armor Spider until you figure out the rolls. The rest are pretty easy compared to other Souls games. The levels in Demon's are pretty brutal and don't have as many checkpoints as the other games.
Also, I think Demon's is the only game you actually ever need to use more than 1 weapon in a run. The miners in Stonefang needing thrust/magic is something I can't think of encountering in any other souls game.
Also because the challenge is in the levels of Demon's, once you learn the levels and the tricks to them, it's fine. I can run through any stage in Demon's no problem right now. So on a replay right now Demon's would be one of the easier souls games outside Flamelurker/Allant fights. But then I could do that 10+ years ago after clearing the PS3 one and I forgot everything in the meantime and on replay this time it was hard as fuck so...
But most Souls games are like that where if you remember the levels, it's only the tougher less-scripted bosses that will give you trouble. If I re-ran DS1 now I'd probably be fine outside a few deaths on the Ornstein/Smough fight.
I definitely thought DS3 was the most accessible. There's a few challenging bosses, but otherwise it's a game you can just blow through on progression. Which isn't a bad thing. Was a lot of fun.