Bhagavad Gita, Chapter 11, Verse 52

The Deity said: Very hard indeed it is to see this Form of Mine which you have seen. Even the Devas ever long to behold this Form.

What Arjun just witnessed is named here as genuinely rare even among beings far more powerful than him.

Krishna states that even celestial gods long to see what Arjun has already seen. Real rarity is confirmed directly, not left for Arjun to assume.