Lexical clarification may resolve an unfamiliar word while leaving other interpretive questions open. A pronoun may still require identification; an allusion may still need historical context. The science of gharīb is therefore one part of tafsīr, not its entire replacement.
It is also important to distinguish lexical sense, a particular instance, and a normative ruling. A dictionary can clarify the general meaning of a term, but its application to a specific historical or legal case may require additional evidence.
Successful explanation is not measured by the number of competing glosses collected. It is measured by a supported, coherent understanding of the intended expression.