Agree about your general "getting better isn't inevitable" and "not all will be better" points, but history has proven when a religion comes to an area, it's not just bringing "illumination", but also a politico-economical selling point. At least in Indonesia, by converting to Islam, some states actually gained at least not so small advantages such as access to huge addition of market complexes across the Indian Ocean for their products and some other things that meant "greater flow of money inwards". Also, Islam and Hinduism has this important difference in viewing this "caste" problem, which sometimes meant a quite radical socio-political revolutions in some societies, radical for that time's standard at least.
How Islam would have changed Taiwan though, is maybe later to be answered after we've finished discussed about "how will Taiwan become Muslim" first. It seems to me that at least since the beginning of Anno Domini era their only most extensive contact has been only with mainland China, and even that in mostly technical sense, for most of the time. To be frank I've never heard of Taiwan making other meaningful contact with other regions, it had been that secluded until relatively recently. Though I'm rather interested about how would the absent of Spanish in Luzon(maybe Magellan never reached Phillipines, or maybe he never defected to Spain, or he died in Morocco/never existed in the first place) would provide some a bit long term potential. But I think that the best way to achieve this scenario, one would have to make a freaking change in China.
