There are plenty of reasons to say that it is. The corpus of revealed prooftexts is closely guarded and ranked by the decisions of hadith critics of old. The meaning of each word is governed by prescribed literal interpretations that must be followed in the absence of contrary evidence. When prooftexts conflict, abrogation settles the matter in favor of the evidence revealed last, freezing the law as it was at the end of the Prophet’s life. Analogy extends the law’s reach to cover every aspect of life, leaving nothing to human whim. And consensus progressively constricts the range of interpretations available to jurists.
Yet consensus, as Ignaz Goldziher pointed out over a century ago, does not in fact freeze the law; on the contrary, it gives Islam its “potential for freedom of movement and a capacity for evolution.” Consensus is rarely if ever a known historical event that precludes further argument; rather, it functions as a rhetorical claim (made only when there is in fact a disagreement) that can be used to support innovations once they are accepted by enough of the Muslim community. And like consensus, many other aspects of legal theory that at first blush appear conservative actually lend themselves in practice to disagreement and change. I argued in The Formation of Islamic Hermeneutics that the set of linguistic rules that prevailed among classical legal theorists did not really limit or dictate interpretation, but instead gave interpreters multiple options. The textual evidence available to them was vast and often conflicting, and the rules allowed them to modify the meaning of any text they found problematic by appealing to virtually any other kind of evidence. The same could be said of hadith criticism, abrogation, and analogy: the apparently clear rules set down by legal theorists seldom actually dictate a single interpretation, but rather provide mechanisms for advancing and defending alternative views. This point comes up repeatedly in my online Critical Introduction to Islamic Legal Theory.
Screenshot from A Critical Introduction to Islamic Legal Theory (waraqat.vishanoff.com) where I articulate in greater detail many of the ideas in this post.
If this is correct—if the actual function of legal theory in the practice of constructing, defending, and debating legal rules is to provide flexibility rather than static uniformity—then it is no wonder that many modern reformers have seized upon uṣūl al-fiqh as their tool of choice. They have massaged and rebalanced legal theory, giving greater weight to non-revealed evidence such as custom (ʿurf) and human welfare (maṣlaḥa), or reframing consensus as something to be produced by legislative assemblies; but most have not fundamentally challenged the structure or function of classical uṣūl al-fiqh, which was already a set of powerful and highly flexible interpretive tools.
Flexibility, however, cuts both ways—and it cuts one way more easily than the other. Almost any answer to a legal question can be supported using classical legal theory, and medieval jurists were adept at arguing that a text meant exactly the opposite of what it appeared to say. However, such creative interpretations sounded plausible only if they were already widely accepted by the community of scholars. It was easy to demonstrate, using the tools of classical uṣūl al‑fiqh, that a full bath before the Friday prayer was only recommended (despite the Prophet’s explicit statement that it was obligatory), or that a wife needed her husband’s permission to go to the mosque (despite the Prophet’s explicit statement that women should not be barred from going), but those arguments carried weight only because their legal outcomes were already taken for granted. Arguing for a radical revision to the law might be equally easy in theory, but in practice it would be quickly refuted and laughed out of court—as the now–defunct Ẓāhiriyya soon discovered. A ruling that supports the status quo hardly needs justification, because the interpretive moves on which it rests have already become part and parcel of the discourse, but an innovative interpretation will be scrutinized at every turn. Thus, while the flexibility of uṣūl al-fiqhsounds promising to reformers, it is not easy to wield persuasively in support of radical reforms.
This does not mean that legal theory makes the law stagnant. It does not actually have that kind of power. Uṣūl al‑fiqh rarely seems to dictate the law one way or another. More often it seems to operate as a rhetorical tool, as the grammar of debate, or simply as an epistemology—as a way of convincing ourselves that what we do know fits our ideal of how we ought to know. If that is so at least most of the time, then uṣūl al‑fiqh does not generate or determine the contents of the law, but rather justifies the law to ourselves and others. That means it has the power to make laws sound more or less plausible, but it cannot really control the evolution of the law. Whatever the community comes to regard as God’s will eventually becomes easy to justify using legal theory. The law of the jurists changes slowly, but in the long run it follows the trailing edge of public opinion, and legal theory follows not far behind.
Legal theory is conservative, then, but not because of any inherent rigidity. The conservatism that really controls the evolution of Islamic law is the intrinsic conservatism of culture—first the slowly morphing social norms of the Muslim community, and secondarily the particular subculture of the juristic community. Legal theory’s most conservative element is its attempt to regulate that legal subculture: the daunting qualifications it requires of a mujtahid ensure not only a certain academic expertise but also a certain cultural horizon from within which all authorized interpretation must take place. Only those steeped in the ethos of the traditional Islamic sciences may have a say in interpretation, while everyone else simply follows along.
That list of qualifications, however, is the dimension of legal theory that is least heeded today. Interpretation is no longer the monopoly of a traditionally trained class of jurists. Legal theory’s one truly conservative feature is losing its grip.
 Goldziher, Introduction to Islamic Theology and Law, trans. Andras and Ruth Hamori, (Princeton, 1981), 52.