The later version cannot be assumed superior unless its new form genuinely replaces or surpasses the original's expressive merits. A concise and transparent earlier image may retain an advantage even if the newer verse becomes more elaborate.
Abū Tammām's “time is miserly with his equal” depends upon one central image. Abū al-Ṭayyib adds the transmission of generosity and then another attribution of miserliness, creating greater conceptual layering but also a more demanding interpretation.
A sound literary assessment should identify the relevant kind of excellence and the purpose of the passage.