What reason do we have for relegating Pelinal's time travel to "imagery" in a world where time travel has been confirmed to exist?
Because it ain't time travel.
The Jills did not have their full powers; rather, I should say, all the mundex spirits had every power at every time amendment at every ordering, which is to say none of them could ever fully express; our world was young and so were its architect gods. - http://www.imperial-library.info/obscure_text/nu-hatta_nu-mantia.shtml
1. In short, gods can control the events in time.
2. Gods controlled time during the Warp in the West (Brass God x7), during the Eruption of Red Mountain (Tribunals Apotheosis), during the Dragon Broke (Selective) and in the Dawn Era (The Aedra).
3. Afterwards when they relinquish control, the Jills combine these timelines. Not in the sense of a gentle merger but dumping everything from both timelines into one. The results are described in Warp in the West as soldiers mysteriously appearing in castles that they seemed to have conquered in the alternate timeline and sand storms comming out of nowhere.
The Dawn Era has the different time lines reflected in it's different origin myths and cultures and massive destruction of Tamriel - there was not a single decided shape for it.
The actual Dragon Broke lasted so long that this part of history became an incoherent mess.
4. As each god only controls the events in time and not time itself, each Dragon Break has a fairly clear start and end.
As they can't control the events outside of the period in which they control time. They can only compress 5000 years into 10 minutes and leave a book from the 4th Era behind, it isn't from the actual 4th Era but from the 4th Era that one particular god created in his time line.
This is a good thing because actual time travel creates horrible paradoxes.