The performance issues are inexcusable. From needs to get better at the technical aspects of development, there's just too many problems: 60fps max, no ultrawide support, shader compilation stutter, poor RTX implementation. From Software aren't the plucky underdogs who shocked everyone with their first few souls titles anymore. They're a industry unto themselves now, they have the resources to solve these problems.
As far as the difficulty goes, I haven't played enough of the expansion yet to reach the "main" bosses. But based on what I've seen, I can see where people are coming from just in some of the side bosses and even a couple of the field enemies. I don't find their long combo chains to be a lot of fun to face-off against, and it sounds like there are a lot of those in this expansion.
The dungeons I've reached have been challenging in a good way and the level design is a step up from the base game. Same thing with the open world areas: they're smaller and more focused, have more verticality and look spectacular.
I like the scadutree fragments system they came up with to ensure that regardless of how much you've leveled up you'll still have to explore the new map to take on tougher challenges. I haven't tried bringing in a 200+ level character in yet. I started with a 120 level character which is a little below the recommendation, but I haven't hit a wall just yet.