Whatever churns you do these days only earn AA miles.
I would say the most "epic" Citi AA churns would be pre-Dec 2011, if you were able to use them not just to earn AA miles but also to earn AA lifetime status (1 million lifetime miles gave AA liftetime Gold, 2 million lifetime miles gave AA lifetime Platinum). In Dec 2011 AA changed lifetime status to only count paid flown miles. (And it was by far the last airline to allow miles from credit cards to count toward lifetime status, since when I started churning AA around 2004 it was already the only one.)
I estimate that I churned over 1 million AA miles between 2004 and 2011 (since I earned a total of 2 million during that time, about 6 months before it stopped working). Maybe that's not as fast as someone with mailers can do it today, I dunno, but doing it back then, even when it was only 25k per card (but two cards at a time every 65 days) with sub-$1000 minimum spends, was "stacking" RDMs plus lifetime status miles back then with each churn, and no one today can do that.
And the race to get to a million mile marker before AA changed how lifetime status works (a change had been repeatedly rumored for years before it actually changed in Dec 2011), there's no long-term race any more (related to churning) than I can see that compares to that.