Not just difficult, but there's just so many of them (for the same company ofc). You could ace 3 interviews and not even be half way through the process. You have to be continually on top form for days/weeks on end.
A lot of these people also have a policy that even one person can fail you. So if you do 8 interviews with 2 people each, then there's up to 20 people in the process that can ruin it for you.
I think LLM performance on previously seen questions like interview questions is too good for it to be allowed. I wouldn't mind someone using an IDE or API docs, but you have to draw the line somewhere. It's like how you can't use a calculator that can do algebra on a calculus test. It just doesn't accomplish the goal of testing anything if you use too much tech, and using the current LLMs that all suck in general but can nail these questions that have a million examples online is bad. I would much rather see someone consult online references for information than to see them use an LLM.