The point is, Sola Scripture proclaims that no truth important to faith formation is to be found outside of the scripture. If that were true, then Sola Scriptura would be itself a doctrine found in the scripture, but it is not, -- no basis in fact.
On the other handm the "faith once delivered to the saints" is a historical fact undergirding the Holy Apostolic Tradition.
Both sola Scriptura and the Scripture/tradition position are objectively unprovable and thus, assuming the definition is valid, is superstition. Ultimately, it is a matter of which position (or for that matter, the position of Jews, Mormons, Muslims, Buddhists, atheists, etc.) comports with one's presuppositions and which position is more reasonable, that is, more in agreement with observation and reason.