Which game is harder assuming you only use a sword and roll? From my memory I recall Dark Souls 3 being a lot harder

Memory and nostalgia are a deceiving bitch.
just to give you an example, i finished ER, beating every single boss, even Malenia.
Today i started NG+, got to Margit and beat him, alone and he didn't even touch me to my surprise.
Meaning that the game inadvertently fucked me so hard that i didn't notice how spastic my reaction time is now against what it was when i started the game.
TL.DR, DS3 must be a joke in comparison right now if you go directly from elden ring.

they're definitely a step up from black knights with decently varied moveset and a phase 2

Elden Ring.
All the elements that made DS3's hardest bosses hard were given to every enemy in Elden Ring. Practically every enemy delays their attacks, has sperg combos that go on longer than you think they will, and can jump halfway across the room.

Elden Ring is harder if you play it like DS3. It's a complete joke if you use all the tools it gives you though. It's also inferior to DS3 in almost every way.

Most correct hot take i've seen in this shithole.
I love the open world concept tho, it's executed poorly sadly.

Elden Ring is tricker, you can get to the bosses far easier but you'll be less prepared. I guess you could just run past every enemy in DS3 to get the same experience but the game doesn't naturally lure you that way, whereas in Elden Ring every fight that goes wrong you instinctively try to horse out.

This, just look at how people are playing the game, its literally the game with the least variety because everyone is using the same shit

If you're just doing sword and roll Elden Ring is significantly harder. Bosses in Elden Ring are all animation delaying, endless comboing, hard tracking, button reading messes. To the point where all immersion is broken when fighting bosses. Sorry seeing bosses literally hold animations for seconds and flying around in the air like helicopters is just fucking stupid as fuck even in a fantasy game.

Elden Ring takes immense cues from Dark Souls 2 (but now it's okay because Miyazaki's name is one it). There are tons of gank spots, numerous duo bosses, and basically every negative thing about Dark Souls 2 enemy design has been turned up to 20 in Elden Ring. The game's balance is also incredibly bad. Dex builds are overpowered, Int builds are overpowered, Faith is mediocre, and Strength will make you want to uninstall. If you play Strength in Elden Ring be prepared to do nothing for 120+ hours other than spamming jump attack.

Dark Souls 3 was kinda easy, save for Sister Friede. I hate that fight.

Why is the dark souls 3 dude giving me a thumbs up?

3 had some shitty bosses, sure, but for every yhorm or deacons, there was a nameless king or pontiff.