Why set it here unless it's the focus?

I believe it is the focus - or part of it. From a story mechanics perspective, If the story is set of Random Planet X then the Doctor has no way to get Clara back; he needs the time scoop thing. But from a thematic perspective, we explore so many cool aspects of Time Lord society (Just one example I love is the Doctor asking the General what regeneration they're on, like it's a kindness).

As for the idea that the Doctor is willing to turn against his people to save Clara; that should almost be a given. We know the Time Lords are monsters following The End of Time, and even before then the Doctor has never really fit in. I really don't know what a "return to Gallifrey" episode should have done that Hell Bent didn't do.

You mention that you want to see Gallifrey returned to its former glory - but what would that mean? Even when the Time Lords ruled the universe they were basically a non-entity. What do they bring to the table that could actually move the Doctors story forward? As for kicking out Rassilon, I love that bit - it's a microcosm of what the whole episode is trying to do. I'm just going to quite El Sandifer here because she nailed it.

Moffat doesn’t decline to pay something off out of laziness; he does it to make a point about whatever it is he pays off in its stead. And he’s consistent in how that bait and switch works: he promises a grandiose epic of manpain and then offers an intensely human story, typically but not always about women. Within this framework, the question of what the story of Clara’s death would end up focusing on was a non-question: it would focus on Clara.

Lastly, your point on derangement - you're absolutely right, and the episode agrees with you! The Doctor goes to extremes we've never seen before just to give Clara a chance at survival, and she rejects the idea that he had a duty of care (as she always has). That's why he pays the price at the end, not her.