Briefly, this is one of the more well balanced assessments of the traditional lectionary's often unnoticed strengths. There are, of course, some qualifications that should be made. The author correctly points out the parallel between the gospel readings of the old lectionary and the subject matter of Gregory the Great's sermons. In this instance, we have some connection to the sixth century in the cycle of gospel readings, however, we need to exercise some caution in that we do not know if the lections that were transmitted to the "Tridentine" liturgy are the precise ones utilized then. Given the tendency towards creeping brevity in the Roman liturgy, it would not be impossible that the lections of Gregory's time were still somewhat longer. This, however, is relatively minor.
There remains, among liturgical scholars, an unanswered question of whether or not the reform of the Roman liturgy (apart from the questions of more gravitas) should have occasioned the development of a three year lectionary. Certainly, I don't think anyone would hesitate to admit that the three year cycle is indeed an innovation based off of modern liturgical theory. Whether or not it was legitimate to do such a recasting of the Roman lectionary is another matter. There is, plainly, little if any precedent for the cycle of readings as it was constructed for the Missal of Paul VI - the modern lectionary is an intellectual construction. Yet, there is evidence pointing to dualing customs in Italy of a lectionary comprised of three or two readings. There is some evidence of Italian usage of a three reading lectionary, although, we do not have a complete cycle to work with. The evidence is, thus far, partial if not fragmentary.
There are numerous lacunae concerning the old Roman usage of the lectionary. We have a fair sense of the Gospel readings during the sixth century due to Gregory's sermons, however, it must be noted that Gregory the Great did a substantial restructuring of the Roman liturgy and it is still some time later before we get a more complete picture of the Roman liturgy. The Roman liturgy, even during Gregory's time, is still murky, more so when we try and peer into earlier centuries. The Hadrianum provides us with a glimpse of the Roman liturgy shortly after the time of Gregory the Great.We can do some reconstruction, but there are still frustrating gaps remaining when trying to create a model of the liturgy at the time of Gregory. The so-called Vernonense Sacramentary provides us with a provocative glimpse into various Mass sets of probable early Roman origin (at the very least, Italian). When studying the content, one is often pained at the losses the Roman liturgy has suffered over the centuries. These pieces of early evidence, however, are concerned only with the euchological corpus. The nature of the lectionary at time, particularly in those elusive pre-Gregorian centuries, remains largely unknown.
All of this is to say that the author's point about the pedigree of the "Tridentine" lectionary ought to be taken seriously, in so far as it has precedence and a historical case that can be made in its favor given the lack of any traceable evidence from the earlier centuries. Additionally, for the careful reader, the author does aptly suggest that onus rests upon supporters of the new lectionary to justify its implementation. The new lectionary is a construction that came, literally, out of nowhere and reflects the thinking of biblical scholarship and currents in theology of 1960s. The perennial value, of, say, paschal mystery theology is disputable, so too its influence on the reform of the Roman lectionary. The new lectionary, far from having an established pedigree, is on the verge of theological obsolescence.