And Star Trek's portrayal of a truly interstellar civilization is an area where there is enormous room for improvement.
That's assuming that what is being depicted in Star Trek is in fact a "truly interstellar civilization."
Instead the Federation is a collection of separate and distinct civilizations, who co-operate for defense, exploration and a few other activities. Members of the Federation could have some (but maybe not much) interaction outside of that, some diplomacy, cultural exchanges, tourism and trade, but largely are not any kind of a collective melting pot civilization.
When we see the species of the Federation interacting outside of Starfleet, it does seem like a great deal of it (
not all) are ambassadors engaging in diplomatic activities.
In fact, I've always preferred it when aliens in Star Trek refer to us as Earthlings. It makes more sense in the context of Vulcans being from Vulcan, & Betazoids being from Betazed, Ferengi from Ferenginar, etc...
Ferengi: "Hoo-mon."
Human: "Wow, that slur really hurt, you know coming from a Fungus-en-gii."
Whaaaaa??? The whole point of a trek is to go somewhere else. It's not about the starting point, it's about the journey and the destination.
But (for better or for worse) Star Trek focuses on Humans, Human lives, Humans in Starfleet, Humans journeying, Humans fighting, Humans exploring. I can remember a small number of DS9 episodes that had no Human characters in them, but to tell you the truth, if a Star Trek series featured no cluster of Humans in the main group, I probably wouldn't watch it.
As to saving present-day Earth from certain destruction (repeatedly) in the theatrical movies, I wish that TMP hadn't set that pattern,
Some of the movies pretty much had to feature Earth, certainly most of the time travel stories.
TMP. Didn't have to involve Earth, the Enterprise refit (hate that term) could have be going on somewhere else. V'ger could have just as easily been heading for Vulcan, and have been a old Vulcan probe. Would this have engaged the general audience? Maybe, Vulcan's probably the only non-Earth planet that would be recognized.
TWOK. Establish the Starfleet Academy as being somewhere other than Earth, change the view out of Kirk's apartment (or not), reuse the Enterprise departure scene from TMP.
TSFS. The ship isn't returning to Earth at the beginning of the movie, the mushroom is in orbit of another planet than Earth.
TVH. The time in the past would pretty much have to be Earth, although this movie would be a great opportunity to establish that the Federation meets somewhere other than Earth, have the Federation President issue the quarantine from another planet (or have it be a Earth official), have the final meeting room be not on Earth.
TFF. Enterprise leaves from not Earth. Shore leave on some random planet.
TUC. Enterprise leaves from not Earth. Change the view behind the President to something else.
GEN. No Earth as is.
FC. The time in the past has to be Earth.
INS. No Earth as is.
NEM. This ones hard to say, to tell you the truth I wasn't aware for years that the wedding reception scene
was on Earth.
ST09. Hard to say about where brat child Kirk on Earth could be otherwise, again have Starfleet Academy be off Earth. Drill into another planet other than Earth.
ID. Have the Earth scenes be a major built up Human colony, one with a starbase.
BEY. No Earth as is.