1.- there is already training duties, they are named Guildhest, they are meant for new peeps to learn in game battle mechanics.

2.- make training duties for specificinstances are pointless becuz their porpouse, Instances were meant to surprise you and amaze you, they werent meant for people to watch a video about how to do it and then re-do, despite this is what everyone does nowdays, but there is always some peeps who did it for first time without watch a video when they were new and experience this sensation of awesomeness.

3.- Im not sure but i think SE meant it for peeps to dont clear new dungeons so easily, i be seen Yoshi-P do some statements as like "we expect gamers to defeat this dutty in 1 week" like with garuda or titan, so means they actually expect for som dutties last a certain period of time before anyone get victor over it.