Looks like it makes sense at the first look, but you can basically use the same logic for literally any heretics, or at least the followers of a heresy if not the inventors? Most likely they probably don't know the truth instead of knowing but denying.
You asked if praying with NO/Vat2 Catholics amounted to heresy. I gave you my answer, which is NO. Other people have said so in various charitable ways.
So what is the heresy that you speak of? It is the hierarchy of the Catholic Church which decides. In the meantime we do our best with what we have and what we haven't. It is not a simple laywoman, no matter how zealous she may be, who defines heresy. As much as you feel, as a neophyte, that you know best, you should learn to eat humble pie and learn from mature Catholics.