Endgame should be challenging - that's the point (from a casual player)

[Granyala]

Not sure with the current fight design philosophy how much this'd help. If you can't avoid piling up vuln stacks, you're toast.

That's super easy.
First of all: increased HP and defensive stats will get you some wiggle room.
Secondly: SE can set the vuln stack-flag to 0 or re-blance the numbers at any time, if they feel the content is no longer viable.

That being said: people that crave challenge have more than enough to do. I see no reason to up the difficulty of the remaining content to savage level as well. Not every gamer plays videogames for challenge reasons. Many just want to relax after a stressful work day.
One playstyle isn't less valid than the other.