Personally (and I can only speak for myself), I don't play games for 'mental stimulation'. I work at a hospital so get all the mental stimulation I need in RL. I play games to relax, to chill out and to not have to think too much about something. I will never do Extreme, Savage or any of that sort of instance, and only do raids when required to by the MSQ. As soon as it's done, I'm out of there, never to return. If I could skip them (including the 8-man duties) and still progress the MSQ, I absolutely would. For me, they are at the upper level of my difficulty range, and I find them exhausting. They are not fun, and I dread them.

As the base game, the MSQ should never be difficult to play through, as it should always be balanced for the absolutely average player. It should give some challenge, to make you pay attention to what you have to do, and even have consequences for mistakes, but it should not be so difficult that the average player gets frustrated enough to leave the game entirely. I have solo duties set to Very Easy so I can get through them quickly to get on with the story - that's what I play for. Having said that, my main is currently stuck (even at VE) at a solo duty that I just can't get through and I will need to wait for a weekend when I have time and energy enough to try it again, several times if necessary. Why am I stuck on VE mode? The duty calls for a lot of running around and simultaneous duty action clicking - I don't have good enough reflexes now and also have arthritis in my hands, which makes things interesting...

I also have no issue with the trust system, and am really enjoying it now that it's been extended to ARR as I can practice my upcoming characters' classes in a 'real' scenario without impinging on other players. Some days I really don't want to have to deal with people, so running a dungeon with NPCs is just relaxing fun.

'Difficult' is very subjective - what's difficult for me is likely to be incredibly easy for you.