Thinkfact, you need to look up the gemara in chelek which appears to allow for the possibility that Daniel could be moshiach, although he was already deceased at the time.
But the main difference is that Paul changed the religion totally, by abolishing all the mitzvos except for a few. (No kashrus, Yom kippur, shabbos, shatnez, sitting in a sukkah, etc.).
The Rebbe ZTL did not change anything, and tirelessly worked to further the observance of Torah and mitzvos his whole life.