Yeah, that’s what I think. Inter Oecumenici (1965) says “The last gospel is omitted; the Leonine prayers are suppressed.” Now, the Last Gospel is part of the order of Mass in the 1962 Missal, but the Leonine prayers are not and never were. The present permission to use the liturgical books of 1962 therefore includes the Last Gospel, but cannot include the Leonine prayers.
As to the suggestion that, when the Holy See says “X is suppressed,” you can just keep on doing it anyway and claim that it is merely a spontaneous outburst of prayer, that must be a joke. What words, exactly, must the Vatican use to be taken seriously? If the Vatican says, “Recessional hymns are forbidden,” do you think a parish should keep on singing recessional hymns in exactly the same way they’ve always done, but claim, “It is after the dismissal! Are you saying that a priest who wants to sing a song with his congregation at some random time (which, by total coincidence, always happens to be as he is processing out of Mass) is behaving illicitly?!”