7290661
Since she bitterly told Celestia "We always did things your way", she is probably deep down mad that she has to retire because of Celestia deciding everything like that(while apparently not bothering to find a compromise for Luna to continue ruling while still being with Celestia).
And from the looks of it often bottles everything up at times. I mean, the NMM mess happened due to she bottled up her negative emotions about being outshined by Celestia and also she kept it underwraps from Celestia about her basically self-harming herself mentally with the Tantabus.

7290667
Still no real proof. And need I remind you that Luna was all smiles during the announcement, even pointing out that there was less and less for them to do?

7290671
She is probably making herself smile to not worry Celestia there. Part of the problems of her basically bottling everything up most of the time.
It makes no sense on why would she just give up being the princess of the night and everything else despite she didn't get to enjoy all of that for much long. Even if there's "less and less" to do, that doesn't mean Luna has to give up being the princess of the night and co-ruler of Equestria.

7290760
"Probably" isn't good enough. Try facts instead of unfounded theories.

Did you forget about "A Royal Problem", where Luna herself admitted her nightly duties were "exhausting"?

7290648
I would hardly call Starlight's backstory tragic, if anything it makes her look like a brat who refused to grow up.

And while Tempest's backstory is somewhat better than Starlight's, it still doesn't excuse her betraying her homeland and working with a Card-Carrying Villain like the Storm King.

7290648
My issue is in people bringing in the real world to justify what happened to the Trio and particularly Cozy - such as, say, the child executed in 1700s Connecticut mentioned upthread as a sign that executing children is perfectly acceptable - but then get uppity when it’s brought up that if you use real-world standards then what happened was a gross miscarriage of justice for a wide number of reasons, chief among them Cozy’s age and the fact that she didn’t get a trial.

You can’t have it both ways. Either you’re arguing from a real world perspective or an in-universe, ridiculous world of magic perspective, but you can’t do both. They’re not compatible.

If she was in Season 1, people would consider her a classic MLP villain and not question why she's iredeemably evil

Speaking of in-universe perspectives, this bears attention for one simple reason: Discord.

Firstly: Discord when he premiered was presented as the anthesis of everything the show was about. He was vain, cruel, selfish, evil, and arrogant. His introduction was loaded with subtle but present Satanic imagery - the stained glass window of him dangling ponies over a sea of fire while we can hear the screams of the damned, natch - and his very name is an antonym to “Harmony” as well as referring not to just to chaos as is often said, but to conflict and strife. It was very plain in “The Return of Harmony” that for Discord, chaos was a means to an end, not an end unto itself (witness his meticulously planned breaking of Twilight, for example, he left nothing to chance there). He wasn’t a mere chaos spirit, he was a malignant, evil spirit.

From a writing perspective, there is no point to redeeming such a character and making him capable of friendship - Discord, the literal opposite of friendship - unless it’s to make it plain that anyone can be redeemed. That there is no such thing as an irredeemable monster within the context of the show.

As a side but related note, The Return of Harmony was written in Season 1 even though it’s the Season 2 premier. There was no plan to ever use Discord again after that point. Any “proof” of redemptive qualities that you see in RoH isn’t actually there, it’s confirmation bias. Discord’s redemption wasn’t considered until Season 3 and was, if I recall correctly, a fan-written episode idea. Which will play into my third point.

Second point: In-universe, Discord displayed mood redeeming traits, none whatsoever, in “The Return of Harmony”. He was presented as purely evil without any care for anyone else. We almost get a scene where it seems like he might, after he’s broken Twilight, but it’s immediately tossed aside as he lets out a triumphant “YESSSSS!” at the shell that Twilight has become and goes on his merry way.

And yet Celestia still takes special effort to try and redeem him, the irredeemable antithesis of Harmony.

Later, when Discord betrays Equestria to Tirek, Twilight Sparkle asks for him back along with all the other Mane-6. At this point Twilight has not seen a hint of contrition from Discord. She knows that Tirek betrayed him, obviously, but she has no reason at this point to suspect that Discord has actually learned from it. Nevertheless she asks for him back even though he had done nothing to deserve it and was in fact the one most responsible for the current situation with Tirek. Discord hadn’t even apologized to anyone yet (not even Fluttershy) and even if he had, he certainly hadn’t to Twilight.

That’s two times that ponies went to bat for Discord. Took a risk. Tried to help him get better. The frickin” Lord of Strife and Conflict who had never done anything to deserve it and who has the powers of a little-g god.

And yet we’re just supposed to be okay with Cozy - a literal child with no inherent powers - being tossed aside like a piece of trash?

Point the Third: You and I both know that had Cozy been introduced in Season 1, then there’d be a never-ending deluge of people wanting her to be redeemed. I don’t know how long you’ve been in the fandom, but this fandom used to make excuses for Nightmare Moon and wanted to see a “good” version of her. We had stories explaining Gilda and Trixie. The entire idea of Discord being merely a mischievous chaos spirit instead of the antithesis of good that the show actually presented him as is a canon creation that simply wended its way into the show, as mentioned above with “Keep Calm and Flutter On” being a fan idea. Likewise Chrysalis having redeeming qualities...well, that’s actually in the show but it’s been massive expanded by the fandom.

There is no reason to think that any fewer people would be okay with what happened to Cozy in Season 9. If anything if we’d seen this little child constantly try and fail to take over the world and in Season 9 but also never seen anyone try and make friends with her for those nine seasons, and she got stoned anyway in the finale, there’d probably be an even bigger backlash

7290799
Doesn't mean she wasn't enjoying her job.
Just because its exhausting doesn't mean she should quit it. Luna was clearly enjoying hers.
By that logic Twilight should quit being ruler due to its exhausting when she ends up feeling like that at certain points.
ALL jobs are can exhausting, but they are also enjoyable and productive and part of one's calling in life.

7290996
Honestly I feel like Starlight's backstory could work.
It was missing some stuff and wasn't executed so good.

7291046
The theories are not "sound", because there is no evidence to back them up. Just baseless assumptions.

7291060
We literally saw Luna ENJOYING her job many times.
It was stressful to her at times but we saw her loving to raise the moon and helping ponies in need in their dreams.
She looked happy when she saw each of the CMC's issues were fixed thanks to her helping them in their dreams.

Its all part of her Cutie Mark.