First off, you have to define what makes a revolutionary leader "successful." Did he contribute to the downfall of Qing? Absolutely. Did he unite the country? Far from it. Were his ideas for China revolutionary? Not quite.

Given that much of his "revolutionary" activities were actually done overseas (he spent a lot of his time gathering support from overseas Chinese; Tongmenghui started in Japan, etc.). Indeed, his three principles did get widespread attention, but none of this was new: late Qing and early Republican revolutionaries had already developed extensive ideas that incorporated democracy and modernisation. I am not sure why you mentioned May Fourth either; May Fourth was a separate entity organised by Peking University students which Sun Yat-sen actually criticized for being too radical and corrosive. I believe you meant the New Life Movement, which was something else entirely.

Moreover, organisations such as the Tongmenghui were, although influential, far from united and hardly successfully "revolutionary" in the pragmatic sense. Sun was a moderate, whilst many other individuals ranged from Chinese anarchists like Li Shizeng to left-leaning intellectuals such as Cai Yuanpei, who would later serve as the president of Beida (Peking University). As a "revolutionary" in this sense, Sun clearly fell way short.

What made Sun successful however, was his ability to gather support, put himself nationally as a leader of a major party contender, and create a party that would later dominate China's political history. Given the social, political, and economic mess that China was in before and after the collapse of the Qing dynasty, Sun was arguably successful in what he set out to achieve. However, it would be doing a disservice to the myriad other revolutionaries to ascribe a disproportionately grandiose reputation to him as so many scholars have done thus far.