I guess my personal opinion is more nuanced than "all TR players want things easy, and all end game players want challenge."
Quite a few people stay at end game and TR, or play multiple toons, or have some toons in each location.
Some TR players enjoy challenge, they just will largely only find groups for the rewards/time crowd.
Some end game players enjoy challenge, and they have a better chance of finding a group for this purpose.
Whether TRing or at cap, the reward structure benefits you for not taking on enough challenge to fail. The routine (easiest) R10 runs are always going to be run, and group composition and quest choice is going to prefer less engaging play with higher chance of success over more engaging play but less chance of success.
I am saying the entire design of the game does not encourage or reward taking on challenge, and focuses on rewards/time. End game would need a different model, with the removal of grind per time and limiting things like bypass timers. This would be better replaced by steady participation, and variety of quests. (Think of dalies that change everyday of the year and pool people into actual challenges, and require largely different group compositions from challenge to challenge). End game needs a different reward structure than TR.