Written tradition doesn’t mean there can be no new tradition, it means the existing traditions can’t be perverted. When you say it should be fluid, do you mean we should lie? Or do you not believe our traditions are true to begin with? If so, what use are they, besides being fodder for enthusiasts?
Discussion
A concrete and immutable tradition is one that relies on a concrete and immutable world, which is not the world we live in. Therefore tradition is to change as the world changes, in response to it in fact.
Traditionally (pardon the pun), tradition has been a set of instructions on how to live.
One can view change as perversion as much as adapting. This is the kind of debate I am not interested in having this late in the evening.
If there is a tradition that says the sky is blue, and we change it to say that the sky is green, that tradition has been perverted. Truths absolutely are universal. They might be circumstantial, but within a given circumstance, they apply identically across all of observable time and space. So actually yes, the world actually is concrete, and if a tradition is true then it should also have concrete foundations.
Otherwise, our traditions can only ever be rough approximations of truths (which is what pre-Bible religions were.)