Emphasis is not restricted to inna. Different particles and constructions can strengthen an assertion according to context.
Inna: «إِنَّ الْحَقَّ وَاضِحٌ» strengthens a report.
Emphatic lām: «إِنَّ زَيْدًا لَقَائِمٌ» adds reinforcement.
Oath: «وَاللَّهِ إِنَّ زَيْدًا حَاضِرٌ» asserts firm resolve with an oath and inna.
Qad: with an affirmative perfect verb may convey realization or emphasis, depending on use.
These devices differ grammatically and pragmatically. Merely counting them does not establish eloquence; syntax, proposition type, and the listener’s state all matter.