They appear to understand what the rules say perfectly well. It would seem that they don't have a beef with the argument itself: merely that they would ban the tactic because it's clever and gets the players a bonus.
I'm definitely not arguing the tactic is invalid. I fully accept your reading of the rules.
My problem is that I'm not interested in taking my game to that highly technical level. Or rather, that I'm enough mindful of bonuses to realize I can't have such a stunt provide the substantial saving of one AP.
But instead of reading up on all of this, and thinking about how to best minmax all the zillions of power combinations, I'm thinking to simply outlaw that use of readied actions.
If I call it a corner case I don't mean "I don't believe it is by the rules". I mean "I can't believe the designers wanted you to benefit from that sort of stunt". I mean "I don't want my game to turn into a series of perfectly executed and painstakingly researched actions where each "mistake" loses you significant benefits".
I don't want Ready Action to play such a large role in the game. Certainly not a role which gives a heavy impression of being a minmaxer's optimization move...
That's my view, at least. Can't speak for others. And I'm certainly not trying to ban this tactic in your game, only mine.
As to how you would go about writing the specifics of the houserule that removes the trick from play, I don't know. I certainly don't intend to go into details, as this 1) forces me to read up on the details of what makes the trick work 2) would probably be abusable anyway.
Instead, a gentleman's agreement not to use ready actions in complex ways where suddenly free APs fall from heaven seems easiest and best.
And of course all players need to be made aware of this before play.
Well then, I hope I wasn't incomprehensible...