The Gemara on this daf discusses the Yom Tov of Shemini Azereth, which unlike the last day of Pesach, is considered its own Yom Tov, requiring a new Shecheyanu. The Midrash calculates the number of bullocks brought on all the prior days of Succos to add up to 70, corresponding to the archetypal seventy nations. The last bullock brought on Shemini Azereth, which is a single bull, corresponds to the Jewish nation.

The Gemara (Succah 55b) explains the theme of Shemini Azereth as follows:

⁦The Gemara cites a parable about a king of flesh and blood who said to his servants: Prepare me a great feast that will last for several days. When the feast concluded, on the last day, he said to his beloved servant: Prepare me a small feast so that I can derive pleasure from you alone.

This touching vignette comparing the intimacy between a King and a beloved servant to the Jewish people can also teach a lesson in the opposite direction. That is, in how we should treat family and our intimate friends differently than other guests by reserving time for them.

There is a well-known story about how Rav Moshe Feinstein ZTL treated his son Rav Reuven. His father was careful to not disrupt his son’s seat at the shabbos table near his father, even when prominent and wealthy guests joined the family seudah.

( https://cross-currents.com/2011/06/23/how-the-gadol-hador-showed-love-to-his-sons/ see comments section for various versions with testimony.) 

You don’t need a Midrash to teach you common decency, and not do you need to be the Godol Hador to be decent. However, perhaps this Midrash was a source for Rav Moshe’s behavior. This would especially be true in the version of the story where Rav Moshe kept the standard even in regard to Talmidei Chachamim of great stature.  As in that case, he certainly would require a source in Chazal.