I think you should probably ask the person who said this to explain what she meant. I don't know anyone who considers canon 603 faulty if by that we mean it needs to be scrapped because it establishes solitary eremitism as a public (ecclesial, consecrated) vocation. Implementing it is challenging (discernment is an art!) and the church must take care in learning to do so appropriately. Some canonists consider it deficient because it doesn't spell out time frames and similar requirements. Still, my own take on the matter is that they have yet to look at either the 1) individuality of the canon or 2) the content of the vocation and the canon that governs it themselves.
An example of what I mean is represented by the canonist who advised the Bishop of Lexington in the Matson case. When asked about using c 603 to profess Cole he pointed out certain legalities: it could be used for males or females; it was lived in relative quietude and remoteness, etc. What he did not apparently consider were the substantive elements central to the canon, the character of the vows and what they called for from the one professed, the history of the canon, or the reason the canon required the candidate to write his/her own Rule and what this entails. In other words, his focus was on only the most superficial realities associated with c 603 to provide a legal loophole; he seemed unaware and careless of the very heart of the vocation outlined in that canon.
On the Perspectives Necessary to Truly Understand this Canon:
Once one begins to look at the canon from theological and pastoral perspectives appropriate to vocations rather than from one dominated by law or legalism in search of a loophole, the canon itself does not look deficient in any way. Paradoxically, it may require supplementation to help chanceries see its scope and depths and implement it wisely, but this is because of the canon's richness and completeness, not because of any deficiency. Discerning such vocations will be demanding and challenging, but not because the canon lacks anything. Rather it is because the solitary eremitical vocation being described is focused, intense, and particularly rare, countercultural, and counterintuitive. What needs pointing out quite often is the fact that canon 603 is at least as much surprising vision and invitation as it is a norm. Hence the way canonists suggest "completing it" often misses the point and even prevents the canon's intelligent (and in this I mean authentically Christian) implementation.
I have already written that canon 603 was meant to raise eremitical life in the church to a new dignity precisely to honor it. cf., C 603 Paradigm for All Hermits. It seems to me that the person you are quoting misunderstands the nature of the term public and sees it in terms of notoriety or something that transgresses the hiddenness of the vocation. That's a shame because in my experience it doesn't really do that. "Public" here has to do with public rights and obligations assumed by the c 603 hermit and entrusted to her by the church. These rights and obligations give the whole church the right to hold certain expectations of these hermits and of the vocation itself. Since the vocation is given by God and entrusted to the care of the Church, and since the hermit witnesses to the very heart of the church that is prayer in the silence of solitude --- a vocation in which every Christian shares --- it is important and completely appropriate that this vocation was raised to a state of perfection or form of consecrated life. It does not replace anything. Instead, it serves all eremitical life, whether non-canonical, solitary canonical, or semi-eremitical as a guide to the essential elements of such a life. Similarly, while it establishes and recognizes some eremitical life as normative, it also affirms the value of all genuine eremitical life.
On Celebrating Professions and Consecrations Publicly at Mass:
Yes, eremitical life is essentially hidden, but it is important that the existence of eremitical life in the church is known and celebrated just as we do with all other gifts of God. Thus, our professions and consecrations are celebrated during Mass --- the most solemn and paradigmatically communal setting we know for the most solemn and communal acts in our lives. Nothing about this demeans the eremitical vocation nor does it detract from its hiddenness. Instead it points to the nature of this hiddenness, namely hiddenness in Christ the Incarnate One of God. During Mass we find the deepest mystery of God's Incarnation both hidden and revealed under the species of bread and wine, in the person of the presider and the assembly, and also, of course, in the proclaimed Word of God. Revelation is shot through with hiddenness and in such celebrations, eremitical hiddenness becomes known for its inextricable connection to divine humility (hiddenness) and glorification (revelation). How appropriate then, that a vocation given to the whole faith community and defined in terms of the revelation of the hidden heart of the church be celebrated during such a liturgy!
In the situation in Lexington, one grace we could point to is that it allows significant attention and reflection on c 603 vocations and the appropriate and inappropriate uses of the canon by a much wider audience than usually discusses or opines on such things. Meanwhile, one of the criticisms made by Catholics reading about the story for the first time, was that the Diocese of Lexington had kept the professions attempted by Bishop Stowe and Cole Matson secret when they were meant to be public matters. These commentators were exactly right in this; they knew the importance of public witness and celebration as well as the betrayal secrecy constitutes.
I believe what was done in Lexington dishonored the vocation in its hiddenness particularly, and it dishonored all those whose own lives are marked by relative obscurity and humbleness and would benefit from the vocation's witness. This is the flip side of the paradox outlined above where hiddenness is intimately linked with revelation and public celebration underscores the normal silence and solitude of the vocation. In this case, however, secrecy was actually a betrayal of the vocation's hiddenness. After all, what the Church proclaims in her public celebrations of eremitical vocations is not the supposed secrecy or anonymity of such lives, but rather, the profound Mystery that is both revealed in and lies hidden at their heart.