It’s my opinion that there is very little ornamentation present in the playing of most Irish traditional whistle and flute players, and they can with no difficulty play traditional jigs and reels etc with no ornamentation whatsover, and do so on a regular basis.
By definition, an ornament is something that is not part of the tune, that the tune can do just fine without, that is added for decorative effect.
There’s little of that in traditional whistle and flute playing, aside from trills and crans, both of which are often thought of as being stylistic devices borrowed from the uilleann pipes.
The seperation of notes of the same pitch by using fleeting gracenotes is, to me, a form of articulation. Traditionally most Irish whistle and flute players chose to articulate repeated notes with their digits rather than their tongue.
Now, if a tune has three G’s in a row and you seperate them with gracenotes, forming a “roll”, how is that any more “ornamentational” than if the three notes were seperated by the tongue? The gracenotes are of such short duration that they’re not heard as notes but as articulations upon the note G, and have little ornamentational impact. Moreover, these “rolls” are not superfluous to the tune but are essential to it. So, being neither decorative nor superfluous, I don’t consider single gracenotes and the rolls constructed out of them to be “ornaments”.
Now single gracenotes which form the initial attack of a note on the beat are another matter. I’m not sure how “decorative” they are but they do give a different character to the attack of the note. What to me are definately “ornaments” are “short rolls” because, at least to me, it seems like they’re never actually necessary for the progression of the melody, and they are quite decorative.
Now about crans, yes they’re “ornaments” I would say, but on the other hand if you play three Bottom D’s in the normal timing of the tune (not shoving four notes into the space of three like a cran) and these three Bottom D’s are seperated by single gracenotes, then that’s not really an “ornament” but simply a way to articulate those D’s.
So anyhow to flip the question around from “how much ornamentation is enough?” to “how many gracenotes are enough?” I would say that enough gracenotes are required to articulate the repeated notes of the tune and keep the tune flowing along on the breath. Without these gracenotes you have Irish tunes in which all the articulation is done by the tongue, which to me doesn’t fit the traditional style on the flute or whistle. No “ornaments” are needed at all.
. Reasoned disagreement is always welcome