"Test of time" is a figure of speech. Does using a nonliteral term make it any less true? That it is iconic is surely relative to a group, period, or culture, but does it being relative make it any less true for that case?
it is being well demonstrated in recent cognitive science that human concepts are all largely based on metaphors and that those metaphors are rooted in bodily experience. Even the sounds and movements of the mouth in forming words relate to the experience of the world that the words so uttered represent.
Time as test - the idea that the longer something persists in our world even against all the known reasons why something fails to persist has some internal characteristic which makes it more robust against those reasons which are like an examination or qualification of the integrity of that thing; this metaphor reflects a newer experience of us that we can use instruments to measure and quantify something and/or administer a set of ritualistic actions or questions to judge the quality of something
What if the person has said "persisted"? According to Google the word persist comes from the latin and is composed of two parts:
per-
sistere
sistere means to stand which is, of course, a bodily experience of being able to stand upright which is subject to the usual forces of gravity and imbalance and fatigue that might bring about an end to that state.
per- indicates through, steadfastly which seems to repeat the idea of 'long in time'. per- is also described as an "intensive"...a word that adds magnitude or significance to the meaning it is combined with. So not just "stands" but "continually stands". Its meaning derives from the experience of wanting to call out the "intensity" of the quality. The term intensive is similarly self-referential...by some initial accident or unknown association, the per- prefix is associated with this greater emphasis. Its presence in the word with sistere or stand acts to emphasize the duration of standing.
The integrity of an object or idea, its persistence, is, therefore, metaphoric of someone or something which stands upright for a long time in a dynamic environment. Persistence, the concept, seems less poetic than "test of time" but it is not...in fact.