Heresy is the obstinate post-baptismal denial of some truth which must be believed with divine and catholic faith, or it is likewise an obstinate doubt concerning the same;
Objectively they are heretics. Therefore, using the word is certainly valid and in no need for correction.
And I still say that earthly worship congregations are too often full of themselves. Any claim to be an earthly organizationally unified body was dropped at the point of the Roman/Orthodox split. And the two sides of that split have mutual sentiments towards one another — that the other is the lesser and needs the one that is the essential which of CO-OURSE is themselves. The appearance of Protestants has given both of those something to sneer at, and they do (though Roman Catholics tend to sneer less).
The most genuinely pious of any Christian faith community scarcely bother themselves with these questions — it is mediocre churchmen in need of bolstered egos that do.
“Objectively they are heretics. Therefore, using the word is certainly valid and in no need for correction.”
That can be argued since they have not been corrected by their (our) bishop. They are in error. They are not be obdurate after correction - which is a requirement to be a formal heretic.