the argument by googolplex gradations seems to me like a much stronger version of the arguments I would have put forth.

You just warmed my heart for the day :-)

But why not use a googol instead of a googolplex

Shock and awe tactics. I wanted a featureless big number of featureless big numbers, to avoid wiggle-outs, and scream "your intuition ain't from these parts". In my head, FBNs always carry more weight than regular ones. Now you mention it, their gravity could get lightened by incomprehensibility, but we we're already counting to 3^^^3.

Googol is better. Less readers will have to google it.