I prefer Paul’s explanation, too. The “what if” seems to twist the knife a little deeper even! As if to say “What if God is as ‘unfair’ as you say? It’s His right!” I always get a lift in my spirit when God’s sovereignty is preached. Puts me in the place of being needy of His kindness, as without it I’m lost.
If anybody is a receiver of God’s grace, it is surely Paul.