the normal content is too easy

[Packetdancer]

You have it backwards. Part of the fun in re-running MMO dungeons comes from knowing all the little routing and pulling tricks and being able to show off your skills. You make a video game dungeon so people can discern which parts are necessary and find the route through. That is not a flaw of the content, that is the intent. Puzzles are not worthless for having solutions!

That is definitely part of the appeal of repeating content for many people, in many games! However, many dev teams will see a difference between "Look at how quickly I've got this down to run it after all my practice!" (e.g., speed-running, which you reference) and people trying to do things in the fastest way possible the first time through.

(Source: Used to work at a game company professionally.)

After all, even if you get the newbie message at the beginning of an ARR dungeon, I rarely ever see people interested/willing in going down those side pathways for the sake of the newbie.

"But people will be rude to new players who don't know the routes!"

Just like how they're rude to new players who want to watch the long story cutscenes in ARR dungeons? No, they aren't, because the community and moderators already come down hard on jerks who ruin the new player experience.

While I'm inclined to agree that it is not the majority of the community, demonstrably there is a subset of players who in fact would do precisely that; the fact that folks would not let first-timers watch the long story cutscenes in ARR dungeons is literally why the cutscenes in the Praetorium were made unskippable.

I will also point out that threads semi-frequently crop up here on the forums justifying why it's okay to force people—even first-timers—to speed-run a dungeon because "I just want to get my dailies over with" and "Big pulls are the only way to make a dungeon a little interesting." (I don't entirely disagree with the second statement, mind you, but still.)

Again: I do not think this is the majority of the community, but it definitely is a sentiment out there.