PAA: What DY is saying is actually very Mistaber and, moreover, removes your question. If we assume that once there is a consensus on an Ikkar Emunah that that means that HKBH would not have allowed a wrong view to become consensus and, therefore, the consensus view is the right one, there is nothing wrong with having argued before the consensus. Yes, those arguing may have been wrong in an Ikkar Emunah, but it wasn’t K’firah because they had no proof that they were wrong. It’s a Machlokes in a M’tziyus that they could not be M’varer, so the Machlokes stands. Nowadays, though, that we know the M’tziyus (by virtue of the consensus), arguing on the M’tziyus of an Ikkar Emunah would be Apikorsus.
(That being said, I don’t know that the Chazon Ish having a Shittah and every 5th-7th grade Rebbe teaching the Chazon Ish and ignoring the other Shittos counts as a consensus, which is what basically happened with a few of the opinions about some Ikkarei Emunah in the last 50 years. But everyone agrees that belief in Mashiach is an Ikkar Emunah, so that’s not relevant here.)