“To tell another Yid who does not follow chabad that if he hasnt learned tanya then his Torah is basically meaningless?”
Who has ever said such a thing? The Rebbe said the Chazon Ish would be jealous that he did not have the opportunity to learn Tanya, which is an important chelek of the Torah. This would be no different than saying someone who did not learn a blat gemarah, or a perek mesilas yesharim, or a X Y or Z will be jealous of someone who did. There is nothing negative about being jealous of a chelek in torah or mitzvos that one does not personally merit. In any case, the point wasn’t to smear the Chazon Ish, the point was to show the maaleh of chassidus even learned by children that it is such a high level that even a great gaon will be jealous of it in the olam haemes. If anything this is also great praise of the Chazon Ish.