If this were true, "heretical" movements (Christians in the Roman Empire, Protestants in the 16th century, Liberals in the 19th century, Nationalists in multi-national empires of the early 20th century) would have never prevailed, because they were "deplatformed" by the powers-that-be with vigor. In fact, they were often even decapitated, not just deplatformed. But they were often successful in the end anyway.

Brute force (and deplatforming is brute force) isn't an automatic recipe for victory in a war of ideas.