That is an interesting question, of whether he intentionally lied for the sake of his people. I wouldn't know whether that would make his actions truly sinful or not, that would be up to God in my opinion.
Maybe he just can't stand people keeps dying all around him, and decide to act. The last dynasty was already on the verge of collapse, famines, plagues, floods, all kind of disasters you can imagine were happening. (And it did collapse in 60 years) There were nearly 400 millions people in China at that time (His kingdom only consist a portion of south-east of China, but dense populated area), if he didn't rise up to lead people in a new way (the reason disasters happening isn't natural causes, but lack of good managements, and corruptions), Most of the 100 million people will die anyway, As proved in Chines history, when a dynasty did collapse, up to 70%, even 90% of the original population died due to war and slaughters. And the resulting famines, plagues. History tells gruesome records, armies used woman, kids as food source, since there is no powerful central government to distribute foods and goods to everywhere, and men were drafted to soldiers, or simply killed. Bodies piles up like mountains. You can't begin to imagine how many people in ancient China were lost, during one dynasty fell, and new one arisen. If it was still the same way of wars this time, than the body counts when this dynasty fell could be an unimaginable 300 millions people.
So if he really IS a prophets and God showed him the vision of the future it might be, as a human being, he should stand by and do nothing? Maybe his sin is not about vanity, hunger for power, but just could not afford to wait, before its too late to teach people in the correct, and slow process. As I imagine he 洪秀全, may said to himself, he rather die a sinner, than let innocent people die, since Christiane conversions before his time all failed. (
"Please forgive me God, I abandon you, but I have to save this people") You may said that he just didn't have enough faith. But faith can't save people. And he did in a sense.
He setup systems about open his government's treasury(聖庫) and buy foods to feed everyone, fighting injustice, against drugs(opium addictions are big problems at that time). in records, even in the official records of the dynasty, says things about their high discipline army, not like those riots in history only know about killing and pillaging. Or records about they bring those hungry an woman/children with the army and feed them, training woman to defend themselves and become soldiers, as the government generals mucking them like woman. (The other option is left them being killed, or BEING foods, I know it sounds terrible, but it has been done so many time in history, its not even funny). And his movement did bring the changes about bring down the last dynasty. Many revolutionists and fore fathers of modern China (Republic of China) are once soldiers joined his riots. This happens in 1850s to 1870s, and the modern revolution finally succeeded in 1911, but began as early as in 1890s. And this time is not to form a new dynasty, and not using wars and killings as means to bring down the government. No 300 millions people die. Those who died sacrificed for their believes and saved the others. Although modern China did sink into chaos for more wars when time comes to 1920s, as the old generations died out.
The emperors in China, usually had very open minds about other religions, but Christianity, it is the only one that's endanger the regime, since it doubts the authentic of emperor being the son of heaven. Emperors will never allow that. As Islamic religions even as a monotheism but claim no such thing as Jesus being the son of god, and founded much later than Christianity, had spread into China with no problems. (large populations in north-west China still do today, and create the movement you might know - East Turkestan(Xinjiang) independence movement, it made big news in 2008 Beijing Olympics). And many Christian missionaries come to China and failed many times (They are allowed to become officials even, but no preachings).
Interesting things about Catholic, and Pope, and even in modern China, Catholic(Rome) is not popular as well, (they are forbidden actually). Not because religious reasons though, as always in history, but a reason of political reason. (Some reasons related to Communism and keeping control about public believes), even other Christianity believes as well, they are not recognized by official as religions. Its a land not easily accepting Christianity.
As for the looks, we are structurally different in average height, facial features, the shape of the skull, the hairs growth on the face, and the hair colored, eye colored, skin color, I don't think any Arabic man, can pass as not being instantaneously recognized in Far-East. We even have words to referring to people from middle-east region 回回人, as once Mongolian Empires rules China, and Mongols conquered some of the nations there, and bring them back, it's so different the Mongolian even have laws to define people from there, its lucky Mongolian didn't conquered Europe, or you might look more like us, Mongols look although not like Han people, but closer than any Westerners. As well as we are easily recognizable in the West. So it really bothers people in the East not seen any reference of them in Bible, for them to accept it as the only true words of God. How can GOD missing so many people.
About Taoism, since it has brand in too much different religions into it, its hard to tell what really is native, what is foreign, but in a way, Taoism affected by Buddhism, Buddhism also affected by Taoism in China, forming a new kind, thus says in my nickname - Zenist 禪宗. It branches out from Buddhism, and receive the philosophy of Taoism. The path to enlightenment can't not be told, but to live by. And the illusion of things around us, the one you should doubt the most is you. Or is it?