We don't need to hypothesize, Chevron was the law of the land for most of our lifetimes until the self-appointed Supreme Court super-legislature intervened. Arguably Chevron itself was the courts recognizing established legislative function with federal agencies that had existed for decades prior. We can see exactly how federal agencies would or would not abuse their authority, and congress really didn't have a problem with the situation as evidenced by the the absence of legislation to change the arrangement.
The legislative failure is really that congress hasn't immediately drafted new legislation to reverse this brazen power grab, discipline the rogue justices, and reform the Supreme Court back into its place as an apolitical branch.