Correct me if I'm wrong but...
We got exactly the same type of content with the Mordrem Vinewrath (season 2) and each of the meta event with HoT (except Verdant Brink).
So i think you are wrong
Marionnette was the first “big map fight” with a very nice soundtrack and nice mechanics. People didn’t like meta event map with boss in HoT so yeah we are not going to have these big fights in LW3…
Yeah, the problem is that these big epic world events were created to last for only 2 week periods of time and then the story would move on. It created frustration for people who weren’t able to get on and play the content, or when the content was difficult enough that if you didn’t get the right group you would constantly fail. It’s always been a bit of a nag to me that I never caught Mai Trin. They tried to create huge map events in this style in HoT, but the repeatability of it naturally makes it seem less epic, because the first time I played Dragon Stand it was a hugely epic struggle to build up your forces to try to kill an Elder Dragon, but the 20th time there just wasn’t much about it that was epic at all, it was just a repeat. So there is something to be said about making repeatable content within the game, but there is also something to be said about the epicness of limited stories. I’m sure that there is a compromise within there somewhere, ArenaNet just hasn’t made it yet.
Even those events like the Marionette could at least be repeated throughout the two-week period.
If you go the Karka Hive area in Southsun, you might notice a giant carcass fossilized in the lava. That was the Ancient Karka. It was literally a one-time fight, concluding the Lost Shores event on the afternoon of November 18th 2012. Either you were there to help bring her down that one time, or you missed out forever.
Vinewrath is almost identical to marionette. We also have Tarir and Gerent which are also in the same vein and are evolutions of the design Marionette laid down.
Then we have Mouth of Mordremoth and everything preceding it. That is far bigger than even Battle for LA and Tower of Nightmares in scale.
The seasons are a lot more instanced based since that was based overwhelmingly the feedback from the community. HoT brought back some of the more epic elements from LS1.