Honestly, if you go back and play the older souls games after Elden Ring, you'll see that they're a lot easier than Elden Ring, unless you summon Mimic Tear for every boss fight, I guess. But on a "player vs boss" scale, the fights in the older games are much easier than some of the later ones in Elden Ring (especially if you factor in the DLC).
The thing that makes Elden Ring much easier is the fact that there is always somewhere else the player can make progress. In Dark Souls, you follow a more or less linear path and if you felt underleveled you had to grind enemies because you could not make any further progress until you pass where you got stuck. In Elden Ring, you can go to a different area completely and make a bit more progress there. From Limgrave, the player can choose to go to Stormveil, skip Stormveil and go to Liurnia Lake, go to Southern Limgrave, or go to Caelid if they're a psycopath. This is in addition to all the helpers From has given players. Strong magic (compared to Souls games), Summons that are available to the player literally anywhere on top of the same Gold Message Summons from the Souls games, two moves that give players i-frames, etc.
Sure, if you play it like its a Souls game then it might seem hard, but if you play it as the action adventure RPG it is designed to be, the game is significantly easier than Souls games.
I get what you're saying, but I feel like you're way underselling how hard the Elden Ring bosses are compared to the Dark Souls bosses (the actual bosses, not the re-used late-game enemies with bigger health pool in random dungeons). I don't think there's a single Dark Souls boss that comes anywhere close to any of the bosses from Morgoth and onward (Fire Giant excluded, obviously). Morgoth, Godfrey, Radagon, Malenia, and all the DLC bosses are much harder than anything the Souls series has seen (unless you count broken/janky mechanics like Witch of Izalith's garbage-tier hitboxes).
I suppose, but the player could very easily overlevel themselves to make the bosses very easy in Elden Ring. Can't do that without a big, boring, repetitive time investment in Dark Souls, farming the same enemies in the same location.
Considering they released at least 5 Armored Core games before even their very first souls-like, Demon's Souls, which was not widely played, I am inclined to disagree.
Nah Sekiro is great. Sometimes I just pull it up and play it a couple of days because it's so satisfying. I think Sword Saint Isshin is supposed to be the hardest boss, and it definitely takes a lot of runs until you have him memorized. But on NG+ I first-, or second-tried him. I think all Sekiro bosses are pretty chill once you know them.
Consort Radahn however... I don't know if I have the will to ever struggle through this fight again