We have a mesorah that Mashiach will come, so Rabbi Hillel’s opinion in the gemara is not practically relevant any more, for whomever brought that up before.
Next, even if Moshiach could be from those who have already passed away, to claim that Rabbi Schneerson, who lived many generations later, is greater than Daniel who was a real navi and whose prophecies are part of our Tanach, or even that he is greater than Rebbi (the compiler of the Mishna), is an absurd non-starter.
And the “Ain sof” line is an even worse heresy than the atzmus stuff. At least the atzmus stuff you could dreidel away with a docheik that is, of course, not the true explanation, but you could at least claim it is.
But saying that any human being is infinite (ain sof) is simply calling them G-d because the only infinite being is G-d himself. That’s it. This is essentially Christianity. Nebach.