What did the Magisterium of Pope Paul VI teach about the the use of the First Eucharistic Prayer, the Roman Canon?
He made a legislative statement which he did not make with regard to the other three Prayers. It was that it semper adhiberi potest. This has a very valuable consequence. It means that a priest who resolves that he will use that Prayer invariably cannot be accused of lacking the true mind of the Church, on the grounds that he never uses three other authorised Prayers. It means that when the same text goes on to suggest that Payer II is most suitable on weekdays, this cannot be held to render the use of the Canon Romanus on weekdays to be inappropriate. To use EP I invariably cannot be contrary to the spirit of the new Ordo Missae, because this provision explicitly sanctions such a resolve. Since this Ordo Missae states on its first page that it is ex decreto of the Second Ecumenical Vatican Council, it cannot, unless the Pope was lying, be contrary to the spirit of that Council invariably to use the Canon Romanus.
The Instructio Generalis also remarks that the Canon Romanus is used opportunius on the Sundays and Solemnities of the year; on the festivals of Saints whose names occur in that Prayer; and on days when Proper formulae are provided for the Communicantes or the Hanc igitur.
There are 52 Sundays in the year; and, by my rough estimate, 53 days covered by the other occasions thus listed. So, on something like a third of the days of the year ... and certainly on Sundays and Days of Obligation ... a strong preference for the use of the Canon Romanus is eminently in accordance with the expressed mind of the Legislator.
Even where the Pastor feels that he cannot celebrate versus Orientem or in Latin, surely he could, as a first step, restore the Roman Canon as the normative Eucharistic Prayer? Another indication of the Mind of the Church: this is exactly what the Ordinariate Missal has done! And I know a very flourishing Church in Connecticut where this is the rule!