Avi, read it again. You are wrong.
You’re also wrong to apply safek d’rabbonon l’kula to put yourself in the situation of safek l’chatchilah when it’s avoidable.
Furthermore, hechsherim don’t simply certify that something is kosher after the fact. They arrange that it should be produced on the best possible manner.
Technically, they can certify a non Jewish produced item with a small amount of treif in it, but the reliable ones don’t. Rav Moshe calls it m’chuar. Chazal say batel b’shishim, but that doesn’t mean you’re supposed to put yourself in that situation, even when technically, ein m’vatlin issur doesn’t apply.