I think the more important issue is that everyone agrees that sufficient grace is granted to everyone to be saved. If people want to dispute how that grace plays out in people's lives, that seems a secondary question.
And considering the Catechism, we can note that apart from discussing the question of Catechumens, it does not settle the issue of how broad "baptism of desire" is to be taken. It merely says that everyone is given the opportunity to be saved, and then says that "we may suppose, etc." Presumably one might suppose some other means as well, such as sufficient grace to explicitly recognize the truth of Christianity before death, for instance. In any event, check the theological qualifications for "baptism of desire" in all of those old manuals. Very few will qualify it as defined and Catholic truth. As I said, that's a separate question from whether or not it's true. I happen to think it is true, but I can't accuse someone who holds a more rigorous view of heresy necessarily.

Whether or not something is a defined dogma, or whether or not something is true, are too different things. Not every denial of a Catholic truth makes one a heretic. That distinction is sometimes missed here.
So too the distinction between an explicit desire for baptism and an implicit desire for it. The teaching on the former is much stronger than the latter. The whole question of how someone with an "implicit desire" can be saved, and whether or not that person would receive the grace for an explicit desire before their death, is a debated question.
Example. Consider the question whether or not explicit faith in the Trinity and Incarnation are required for salvation. That question has not been settled, even if one can quote a lot of authorities that seem to be implying that an explicit faith isn't necessary. So too the debate viz a viz implicit vs. explicit desire for baptism, I'd think.
One could maintain the position that everyone who doesn't have the opportunity for hearing the Gospel is given some interior illumination or somesuch. The whole area is unclear, but I think the tendency today to assume that everyone's in good faith and on the way of salvation is deadly for the missionary spirit.

RULE 3 VIOLATION.

The dissidents on this issue are technically known as Feeneyites, though I seem to recall a certain amount of debate as to whether they correctly represent the beliefs of their founder (ie, have coopted someone who was only faintly heterodox on the subject, or who retracted on being reproved by his superiors). Again, not an uncommon problem with heretics.