And the first moment I mentioned, Lando arriving with the cavalry, has been documented to have been in the movie from the very beginning: it was in Colin Trevorrow’s “Duel of the Fates” draft, written before Endgame even started filming. So that obviously couldn’t have been Endgame inspired.
It’s also in Lord of the Rings, when the Rohan army arrives at the last minute to turn the tide of the ongoing battle at Helms Deep. That goes back to the 1960s.