People who keep calling DaS3 or ER challenging or difficult, or who keep barking "git gud" whenever someone criticizes the design of those games are missing the central fucking point: Difficulty is only a positive thing when it's well designed.
You can arbitrarily make anything difficult in dumb ways: e.g. you can require that someone jumped 5,000 times before fighting a boss in order to win, or you can make a boss have random attacks every single fight, etc. This doesn't make something challenging in a good way.
Yet DaS3 and ER are challenging in exactly this kind of way. Bosses have a completely different physical reality than your character: they do not have stamina restraints, they can have nearly infinite combos, they have hitpoint bars orders of magnitude higher than you do, they do tremendously more damage, they move completely unrealistically while being so huge, their attacks magically follow you and are AoE in most cases, their range magically changes to huge distances regardless of actual weapon reach.
In addition to this, many attacks are badly animated, ie there is very minimal telegraphing, such as windup animations, or windup animations are fake and disconnected from the actual attack, which comes out at ridiculous speed. This makes these games much tougher for many players who don't have the best reflexes, and is a strange design choice in 2020s, when many gamers are no longer in their 20s.
A good video game combat system should be one that has consistent and logical general principles, that the player can get better at by practice. And once they get better at it, they theoretically should be able to face any new enemy and know how to fight them. More challenging enemies should just be better at those general principles and force the player to hone their own skills within that text. But in ER, every new boss fight exists in a vacuum, and forces the player to die a bunch of times to learn the custom bullshit of this particular boss.