9 Nissan (Pesach)

The Haggada proves "Vayotzienu Hashem Mimitzraim- Lo Al Yedei Malach...Elah Hakadosh Baruch Hu Bichvodo Uvatzmo" (And Hashem took us out of Mitzraim- not through an angel...Rather it was Hashem in all his glory himself) from (Shemos 12,12)"Viavarti... Vihikeisi Kol Bechor.... Uvchol Elohei Mitzraim E'eseh Shfatim Ani Hashem" (And I will pass... And I will hit every first born... And in all the gods of Egypt I will execute judgment. I am Hashem). All that we see from there is that it was Hashem himself that killed the Egyptian first borns and destroyed the idols. That's not a proof that it was Hashem that took us out of Egypt so why do we try to prove from there?