Chevron is about the statute saying something vague like "a term in a consumer credit contract is void if it is oppressive" and then the effective definition of the word "oppressive" being able to be "interpreted" by executive agencies at their whim with the courts being powerless to intervene. That is contrary to the rule of law. If there is a vagueness, that should be filled by a court supplying an interpretation and that precedent is then established. Law should be stable and predictable.
Remember the original Chevron case was based on the EPA changing its interpretation of "source" of air pollution under the Clean Air Act 1963 to make it much narrower. There was no statutory power for it to do so. Nothing in the Act authorised it. It unilaterally changed its interpretation of the law, and the Court said "that is fine, it is ambiguous, you decide what the law is and as long as it is a reasonable interpretation that is fine". Nothing to stop them turning around the next day and changing their interpretation again.