Complete Parsing of the Qurʾanic Excerpt

Mubtadaʾ and Khabar — Definition and Foundational Rules

وَلَعَبْدٌ مُؤْمِنٌ خَيْرٌ مِنْ مُشْرِكٍ
وَ: conjunctive/resumptive particle (according to context).
لَـ: emphatic lām of initiation.
عَبْدٌ: nominative mubtadaʾ.
مُؤْمِنٌ: nominative naʿt qualifying «عَبْدٌ».
خَيْرٌ: nominative khabar.
مِنْ مُشْرِكٍ: prepositional complement related to «خَيْرٌ».

The predicate is «خَيْرٌ», not the descriptive word «مُؤْمِنٌ».