Here we go with the deflection again – the reason why it’s not apikorsus to teach that, for instance, keeping shabbos is a bigger deal than coming late to davening, is because it’s true! But if someone were to say that coming late to davening doesn’t matter, when chazal say it does, then yes, that would be apikorsus too.
My assertion that shluchim say tznius isn’t so important is based on this thread and your statements that it’s not an ikkar. That explains what we see in crown heights whenever outsiders, “snags” like me drive through it and have to keep our eyes open so as to drive safely.
Tznius is the lifestyle of a Jewish woman. An illiterate woman who can’t pronounce tzimtzum but dresses tznius and behaves modestly is infinitely greater than a woman who studies seforim not intended for her but does not commit to serving Hashem by performing her essential mitzvah. Her studies are, in fact, harmful to her.