There is no doubt in my mind. The Bible is the single greatest hurdle they have had to deal with. They’ve done that by ignoring/rewriting it.
Their second obstacle, of course, is two millennia of church history and the bulk of current world Christianity rejecting what they are proposing. They are in rebellion, so that reality is simply pushed aside.
Tradition is easy to overcome because it can be rewritten. But the Truth will stand until the Day of Judgment.