This is perhaps the most famous verse in the entire Vishwarupa Darshana — and one of the most quoted in all of the Gita. Sanjay says: if a thousand suns were to rise together in the sky at the same moment, their combined brilliance might — just might — approach the radiance of that great soul.
Notice the careful language. Sanjay does not say a thousand suns would equal the radiance. He says 'sadrishi sa syat' — it might be similar. Even his most extreme comparison falls short. He is using the brightest thing a human being can imagine — a thousand suns blazing at once — and admitting that it is still only an approximation.
One sun lights the entire world. One sun is too bright to look at directly. Now a thousand, rising together, their light merging into a single overwhelming blaze. And even that is just a doorway into understanding what Sanjay saw. The verse does not describe the Vishwarupa. It describes the failure of all comparisons to reach it.