In short:

There must be some way or ways to remember dreams in detail and efficiently without writing them down. What is it?

At length:

They seem to fade without writing them down. Personally when writing them down i remember multiple dreams a night sometimes and pages of detail.

When i stop writing though i remember maybe one fragment a week.

There are and have always been people and even entire societies who place great value on dreams who do not have writing at all. So how did they remember their dreams?

If writing were required for all but a small portion of the population (those blessed with a natural vivid dream memory are not very common) to remember any significant amount of dreams then there wouldn't be as much dream tradition in cultures without writing as there is.