You ask about “independent sages”. The only person I can think of whom the perennialist authorities would regard as a genuine master, but who seems to have been unaffiliated with any revealed tradition, is Plotinus. One recalls his response to Porphyry’s suggestion that he attend a Christian liturgy, since there would be angels there: “It is not for me to go to those beings, but for those beings to come to me!” He, and perhaps a very few others, are exceptions that prove the rule.
Though one must of course grant that such a possibility exists in principle, it is nonetheless obvious that a man is a fool if he refuses to take advantage of the sacramental protection of an orthodox tradition on the grounds that he might himself be among so selective a group. Those who suppose themselves the equals of a Plotinus, with angels running up and down the ladder of their being, would be well advised to ponder Schuon’s admonition: “Metaphysical intuition alone does not prevent titantic falls.”
It is one thing to have glimpsed certain truths, and even to be able to convey them to others; it is something altogether different to be wholly transformed by these truths—to know That Which is by virtue of having become That which knows. Don’t make the mistake of equating a planimetric understanding with a truly global realization.