Learn English – the origin of the idiom “have been had”

Your source World Wide Words makes the point that the phrase right as... has appeared in many forms over the years and that right as rain probably became the favoured variant because of its pleasing alliteration. It seems like a reasonable conclusion and all I can do here is add further support to his theory from an earlier example.

This is from In the Midst of Alarms by Robert Barr, 1894:

"To whom are you engaged? As I understand your talk, it is to Miss Bartlett. Am I right?"

"Right as rain, Renny."

Perhaps it was a phrase that was already in common usage at this point but the triple alliteration here is striking.

It’s true that this expression is in an interrogative form that is not normally found in contemporary English. It uses inversion rather than the auxiliary verb do. We would normally expect What do you have? (or, in the UK at least, What have you got?) It’s a colloquial way of saying, in the Oxford English Dictionary’s definition, ‘anything else (similar) that there may be, or that one can think of’, or even, simply, etcetera. It’s of US origin, and the Oxford English Dictionary’s earliest citation is from the 'New Yorker' magazine in 1925.