Dupont certainly did put up a fight. But the Spanish resisted his assaults with great courage and effectiveness, the French ran out of water (in Andalusia, in July), the Swiss defected .... Dupont was defeated at Bailen. His options were retreat or surrender, and retreat does not seem to have been possible at that time. The Convention of Andujar was not an excessively dishonorable surrender, but it was an unprecedented public relations disaster for NB.

The Convention of Cintra, on the other hand, was easily spun into a French victory - a mere temporary regrouping in order to defeat the enemy even more thoroughly.

As far as holding a grudge goes, Dupont had apparently compiled a very long enemies list while imprisoned; when Louis XVIII named him minister of war after the restoration, Dupont engaged in such a thorough house cleaning of the French army that the king was obliged to request his resignation.