«يَشْعُرُ زَيْدٌ وَيَكْتُبُ عَمْرٌو»
Zayd composes poetry, and ʿAmr writes.
A literary connection between the activities is plausible, though the context determines its strength. Conversely, «زَيْدٌ طَوِيلٌ وَعَمْرٌو قَصِيرٌ» links the clauses by contrasting their predicates, provided that comparing the two people is relevant.
A jāmiʿ therefore need not be similarity; contrast may also unite propositions when the discourse intends it.