AviraDara: “no one thought of it as a huge holiday until present-day chabad.”
Its an ambiguous statement, but if your intention was to say that even in chabad, no one thought it was a big yom tov until “present-day”, then you couldn’t have been more mistaken; 19 Kislev has always been celebrated in chabad with seudos, yom tov clothing, no tachnun etc. This was passed down by tradition through the 7 Chabad Rebbes and generations of Chabad families.
If your intention was to say that it was never considered a yom tov in the velt, until present-day Chabad made it one, then that is also not entirely accurate. Other chasidishe kreizen also considered it a personal yom tov for them, as the taanos the misnagdim had on Chabad were also on them. The alter rebbe was picked due to his particular influence in chassidus at the time. Chabad has also always made it a point of spreading chassidus through farbrengens on 19 Kislev.
It is true, however, that there is more of a fuss nowadays in regards to 19 Kislev, but that is the case with every long-held initiative Chabad offers nowadays, the reason being that the Rebbe, in general, always brought Chabad’s ideas to a much broader scale than his predecessors. There are also a lot more Lubavitchers now than there’s ever been, so you’re obviously a lot more likely to hear 19 Kislev then if you’d live in “olden-day” Chabad.