I hope 7.0's has a way to skip most of the current story

[Iscah]

It's also ridiculous to throw someone into the deep end without anything to help ground them.

It's not tossing them in the deep end to start them off at the beginning of Season 2. There would, hypothetically, be a new plot arc starting and the core concepts explained within the new section of plot that they begin from. At the same time, they would naturally pick up the basic personalities of the characters from interacting with them, and can choose to read deeper into their backstories through the Unending Codex if necessary.

If they want to get every scrap of story detail, they need to start from the start. Or they can choose to skip over it and start at a later point in the story, at the expense of missing some details. Catering to them shouldn't come at the expense of sacrificing the story structure for the long timers.

If you do a side quest in the game that theoretically happened before an event you've already done we don't come crashing to a halt, particularly if that side quest isn't hyper generative (as in it doesn't get referenced itself too much, or at all- even if itself references a lot).

The thing with those side quests is that they stay in that one piece of the timeline where they are set. At most you have multi-part narratives like Ivalice into Bozja, but their progression is gated by MSQ so you can't just follow the Bozja storyline disconnected from time also passing in the main story.

If you introduced a whole second thread of MSQ branching off from Heavensward, the world is stuck in Heavensward time frame. You can't reference anything from after it, can't call on the regular cast from Endwalker, have to wall it off as a fully separate plotline that will never cross. I just can't see it being worth the loss to the core experience of the game being one long-running narrative with a clear progression and timeline from one story to the next.