Tackling both “TROS doesn’t pay off Luke inspiring hope in TLJ” and “the galaxy fleet showing up doesn’t feel earned” at once…
In TLJ the galaxy and even the Resistance has lost all hope, only for Luke Skywalker to show up suddenly, right at the last second, and then he inspires hope across the galaxy. TROS only happens after TLJ, so it isn’t hard to draw a connection between the two - they’re only rising up because LUKE inspired them.