Consider that what you consider to be Marian heresy has been part of the unbroken historical patrimony of the Church from the earliest days, and only tagged as “heresy” by relatively late-comer theologians from the 1500’s to the present. Where was their authority for their pronouncements, given the promise of Christ to be with and preserve His Church *all days* till the end of time? Who gave then the authority to switch allegiances from the Church founded by Jesus Himself? They could only have exercised such self-anointed and late-blooming authority had Christ failed to live up to His promise, but that would make Him a liar, wouldn’t it? If the Church became apostate, then we are ALL fooling ourselves, Protestant and Catholic alike, for Jesus could not be who he said He was. We are ALL chasing an illusion and all our hopes are vain. If the Catholic Church failed, then ALL of Christianity is false, for anyone saying what Jesus did in Matthew 16:18 and Matthew 28:20 could not fail in those words were He God, and failing (according to you), could not be who He claimed to be.