In fact, the future shown in the episode could have represented a fork that would occur if they did not undo the fracturing.
Well, there’s one future time period shown in the episode (which was maybe a tad risky or thoughtless of the writers?) … it’s far in the future where they’re still in the Delta Quad and Icheb and Naomi Wildman are adults and Chakotay and Janeway are long dead. I think the implication is that they’re dead because of the temporal fracturing, but I don’t recall if that’s made clear.
Nonetheless, that this future time period doesn’t occur, given Endgame, implies that you’re correct. Not sure if Endgame being caused by Future Janeway coming back in time means you wouldn’t see its effects when traveling forward in time from a point before Future Janeway’s arrival.
Otherwise, the episode is suggestive, especially given how much of Future Janeway is mirrored in Shattered’s past Janeway, that alterations caused by this episode lead to Future Janeway’s intervention, even as seeds in Janeway’s mind that eventually take root .