Buddhism is just realism. Regarding the idea that sages can, "above and beyond interpretation" directly and infallibly see "the ultimate truth", consider the following from Stephen Batchelor. After Buddhism Yale University Press. Kindle Edition, where he is discussing the "two truths" idea:
"The Theravāda tradition, whose teachings are based on the Pali Canon, sets forth a similar view. The late British scholar Maurice Walshe declares, in the introduction to his translation of the Long Discourses (Dīgha Nikāya):
An important and often overlooked aspect of the Buddhist teaching concerns the levels of truth, failure to appreciate which has led to many errors. Very often the Buddha talks in the Suttas in terms of conventional or relative truth (sammuti- or vohāra-sacca), according to which people and things exist just as they appear to the naïve understanding. Elsewhere, however, when addressing an audience capable of appreciating his meaning, he speaks in terms of ultimate truth (paramattha-sacca).23
In reading Walshe’s text, we could easily get the impression that the Buddha himself spoke of these two truths in his discourses. Yet nowhere, not even once, will we find a mention of either sammuti-sacca or paramattha-sacca in any of the hundreds of discourses attributed to Gotama in the Pali Canon. It is not just that Gotama failed to use that particular terminology; he simply did not think along such lines. As soon as “truth” is parsed in this twofold manner, it becomes difficult to resist slipping into an ontological mindset. “Ultimate truth” becomes a signifier of what really is, whereas “conventional truth” signifies merely what people agree upon as true and useful. What may be the earliest mention of the two truths is found in Points of Controversy (Kathāvatthu), a polemical Buddhist treatise compiled in the centuries after Gotama’s death. The Buddha, the author declares:
spoke two truths, conventional and ultimate—one does not come across a third; a conventional statement is true because of convention and an ultimate statement is true because (it discloses) the real characteristics of things.24
To claim that “ultimate statements” describe the way things really are as opposed to how they conventionally appear is ontology. Yet the Buddha to whom I am drawn in the early discourses is not an ontologist. He has no interest in providing an accurate and final description of the nature of “truth” or “reality.” He warns repeatedly of the dangers of getting sidetracked by metaphysical speculation of any kind, of being caught in what he calls “thickets of opinion.”
As for what Gotama thinks of those who talk about the “supreme” (parama), we only have to turn to the Chapter of Eights, the text cited earlier as an example of a skeptical voice in the early canon:
The priest without borders doesn’t seize on what he’s known or beheld. Not passionate, not dispassionate, he doesn’t posit anything as supreme. One who dwells in “supreme” views and presents them as final will declare all other views “inferior”— he has not overcome disputes."
You mentioned you are unfamiliar with secular Buddhism; Batchelor is one of its chief proponents.