This subject of authenticity is something experts and critics love to chew over. There are no recordings of 18th century concerts, of course. There are, however, reproductions of 18th century instruments. There are contemporary accounts of some of the details of musical taste and interpretation. Conductors can make educated guesses about sound from the number of musicians that Handel used, the size of the performing space, etc. All of these ways of knowing are based on forms of evidence that are one step removed from the music on the page and the words beneath the music. It is in the deep thinking about the expressive potential of notated music that I believe Nic McGegan soars!
I have listened to many live and recorded performances by Nic. I've sung in several concerts he conducted and have seen firsthand the way he releases the expressive potential of the details in the scores. The question critics may pose is, "how plausible is it that such attention to detail ever took place in the real-world performing conditions of the 18th century?" Put another way, "Is Nic McGegan over-expressing what is in the score?"
These questions came to mind the first time I worked with him. The details were refreshing in ways I had not heard before. The overall integrity of his conception was compelling. While he is not the only "leader" in the pack of 18th century specialists, he is distinctive in the way he conceptualizes the sound. Other leaders are distinctive, too. That is in the nature of leadership at the top level. I love them also. I would not say flatly that I think he is better than his peers; only that I am more refreshed by his renditions, more thrilled by what I hear in his concerts, than I am by the others.
If you want to hear what I'm talking about, borrow his recording of Rameau's music from Nais and compare it with any other good recording. You'll instantly hear differences in the "thickness" of the sound and in the balance and in the ornamentation and in the phrasing. You don't have to pick a winner; you may actually love contrasting approaches to the same pieces, as I do. But if you compare them, you will begin to hear what is distinctive about Nic's gifts.
I've about finished my first listening to the full recording of Handel's Ariodante. I've got another full recording lined up to go through the same opera, start to finish, with another five-star ensemble. I may have more to say on this subject as I get deeper into these performances.