It's more complicated than that, because there is no "ultimate" or "final instance" in that sense, just a dialectic between the two terms: the test of theory is practice, but the test of practice is invariably theory. The contradiction never comes to rest. One of Adorno's enduring contributions is that he pointed out how the 19th century radicalisms were dependent on that ultimate instance - the wizened dwarf of theology, as Benjamin put it, a.k.a. a theologized scientism - which later turned into the frozen dogma of the national mass-party or cadre state. (This isn't an argument against mass parties, which can be wonderful things, but the theoretical reminder that parties aren't immune to historical processes, and can acquire all the pathologies of the society they are nominally trying to change).
Theory (small "t", the collective property of humanity, as opposed to capital "T", its academic credit-form) is just the body of texts, concepts and narratives at our disposal for classifying and mapping reality. Limiting it to academic works is like limiting works of art to whatever is in the museums.
-- DRR