[Ericson2314]

You are confusing the interval from the previous note and the interval from the root. The millennial whoop might be a minor third, but that in no way makes the chord more minor. And I think plenty of non-musical people would characterize the "millennial whoop" as annoyingly upbeat, most the time, so claiming it is unlike the Picardy third for that reason isn't putting theory ahead of empiricism.

"Mode mixture" where the minor 4 chord is "borrowed" in a major context however is basically stealing the picardy third sound for an otherwise major piece. "American Boy" would be a pop song that uses this very well.