I think the most poignant sin would be teaching of false doctrines such as setting a time on Jesus's positioning in heaven. (1914)
From that single doctrine alone many doctrines or teachings stem and branch off such as the End Times, Great Tribulation and Armageddon all to occur concurrently one after the other.
Which brings up the question did god actually chose these men in 1919 ?
Or were these men so pressed to have something to sell in countable numbers to the public through the literature they published, they disregarded the bible and the guiding instructions given by Jesus in preaching his Gospel ?