In مُسْلِمُونَ / مُسْلِمِينَ, the stem of «مُسْلِمٌ» remains intact: a sound masculine plural.
In رَجُلٌ → رِجَالٌ, the stem changes: a broken plural.
Result: In «جَاءَ رِجَالٌ», the nominative sign is ḍamma, not wāw. Do not impose «ـُونَ / ـِينَ» on every plural.
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Noun Case Classes: Type 6 — Sound Masculine Plural and Related Forms
In مُسْلِمُونَ / مُسْلِمِينَ, the stem of «مُسْلِمٌ» remains intact: a sound masculine plural.
In رَجُلٌ → رِجَالٌ, the stem changes: a broken plural.
Result: In «جَاءَ رِجَالٌ», the nominative sign is ḍamma, not wāw. Do not impose «ـُونَ / ـِينَ» on every plural.