Did you really play those games? Because what you say sounds like a second hand opinion.
You do need to pay attention to bosses patterns, but overall mechanics aren't demanding.. and most importantly - they are reused.
You have a dodge with huge amount of iframes, you can block a lot of attacks(especially in newer games) etc.
There is no need for perfection.
And you can always grind for more endurance and vitality in souls games.
Take a step back, observe the enemy, gauge the distance.. and adapt. but don't panic.
Sekiro was hard yes, but it was fair. It was more of a rhythm game to be honest, than an action one, and they added stealth as an 'equalizing' mechanic for open world content. And honestly it has a lot of tidbits that i bet most people didn't notice(Ogre being afraid of fire for one, bull being scared by firecrackers etc) that also help you greatly.
Some fights in Sekiro were really hard, but satisfying to finish - Isshin comes to the mind, and the Demon of Hatred. If some boss seemed unfair, or harsh, its because you didn't adapt to it properly - they gave you prosthetics that counter a lot of them(umbrella for block and counter, spear to pull out centipede from dead monkey, firecrackers etc). That game just punished trying to brute force it.
Also judging by how game reviewers play games(DOOM footage comes to mind).. it would be akin to listening to fresh junior JS dev opinion on state of linux codebase.
Furthermore there is a fair chance that the game just isn't made for those people. Not every product needs to work for everyone, or you'll just end up with mediocre sludge of similar games.