No one explains why all the races have different names
Because that world is disconnected from Eorzea and grew to have its own culture and standards yet it's still a reflection.
they just expect you to already know how the world and it's culture work before the story even starts.
Well yes, you are not supposed to reveal you're from another world, yet since the exarch pulled you into the first with about as much warning as the people in hiroshima got of an atom bomb you need time to learn it; it's why your first encounter with "different race names" has the hrothgar doing the exposition be absolutely puzzled that you don't know how races are named.
As for culture at large it's pretty Eorzea lite, only exception imo being Runar and his forest hippies where their entire way of living is tied to the state of the world; I can't even give points for originality on eulmore because we have the Ul'Dah syndicates in eorzea for "disconnected rich fucks", Eulmore is just the logical conclusion of how a slow doomsday scenario would hit those people.
I'd say my issue with ShB in this regard is that for a world entirely disconnected from the source the culture is fairly samey, races have different names is quite a lazy attempt even if it makes sense.
They don't even mention that the world is in perpetual daytime until everyone freaks out over seeing stars again.
They do, there's a cutscene shortly after you arrive to the crystarium and go to rest which shows the perpetual daytime and the NPC that serves as the lodging's owner makes mention of both it and that the room is outfitted with curtains for the express purpose of sleeping.
The flood of light is such a poorly explained concept and doesn't really answer wtf happened to the world.
They go plenty on this with the void pre ShB, tough you don't know it as a reflection until later I believe, there's plenty of instances throught the game where an imbalance of aether displays nasty side effects, the most notable one being sastasha where pirates start getting mutated and have tentacles or barnacles growing on them.
Even then and just in case it wasn't fresh on your mind we get a massive exposition dump multiple times explaining it, as wishy-washy as the mechanisms are (i.e. the ascians just cause a massive increase of one aspected aether because fuckitidontknowtheycandothatnow and then it magically just transfers to the source after they open the plot faucet I GUESS.) there at least is an attempt, as for the effects of said floods there's plenty of backstory on what happens and their effects on a world, they're called umbral calamities and the source has gone through multiple, the only "new" aspect ShB onwards introduces is that reflection floods can go wrong and thoroughly ruin a world which somehow prevents ascians from using the plot faucet.
It's so heavy on plot armor to make things happen
Far as I know the only real asspull it does is during the Emet Selch confrontation (ok and maybe Thancred's super mega special stealth vs Ran'jit) and even then that's just "anime protagonist solves everything with the power of friendship" which is standard fare for JRPGS.
. I think it's interesting to have a character who is trying to deal with grief and her own feelings of inadequacy by trying to take on an alternate persona. When faced with overwhelming pressure she has to learn to grow past those feelings and rediscover what it means to be herself. She's uncertain, and clearly struggling but she is clearly more capabale than she believes and learns that she doesn't have to carry her burdens alone.
Lyse sounds great in summary but then we got a whining woman-child who would rather sulk and mope for the better part of an expansion instead working to get over it, I also don't see what qualifications she has to be the face of the resistance other than "because plot" and "because dad/sister", she just gets shoved in there by the plot and hardly earns it.
Summaries and how the story actually handles it are different beasts, she's a great example of it, and to top it all off we had a much better and developed candidate to lead the ala migghers to regain their freedom than eleventh hour Lyse:
Raubahn is already dealing with pretty much everything you mentioned (except the taking on an alternate persona), he's a native ala miggher and open about his feelings for his homeland, and he one ups Lyse hard in terms of developing a political plot since he's had to deal with the ugly side of the ala miggher resistance in the form of extremism, his missing arm being a constant reminder of just how bad it can get; not only this but he even struggles internally with his allegiances (SB does play on this hard, it's a point to its favor) having his heart torn between his duties to Ul'Dah and his wishes to lead ala migghers to prosperity.
They were clearly segmented into different acts so you weren't juggling them.
The first time you get whooped by Zenos in doma you get yeeted into ala mhigger plot shortly after with nearly no resolution, he is then moved back to ala mhigo just so you can conveniently take over doma and bring the plot to an end with La Resistance, it most definitely could have been segmented better, and I know they are capable of this because they did it with the post-SB quests.
Barely any in the expansion itself, every nation that involves itself in the war just agrees to help because the WoL is there (iirc there is a quest in which you literally nation hop and ask for troops, they give a bit of an excuse and immediately go "well but since you're the WoL we're sending some, also please give me your autograph"), Doma itself gives you a walking plot device in the form of Hien (tough at least you and him have to put in work to regain control, so it's not too bad) and the whole Lizard quest, while definitely fun and enjoyable exists as a way to CONVENIENTLY muster troops because you just happened to arrive on the steppes RIGHT AS THEIR KHAN SELECTION WAS HAPPENING, and it just SO HAPPENS that the highly isolated and nomadic Xaela culture allows complete fucking strangers to take part in it so long as one of the tribes says "they with us lmao" and you clear one dungeon, it's just to convenient their entire cultural backdrop has that one loophole to let you become the Lizard King.
I don't even think SB is shit (much as I say it, I like to exaggerate for shits and giggles), but there's enough wasted potential and some few points of unbearable horseshit in there to sour it for me, and this is without going into great detail about how the best bits of political intrigue relating to ala mhigo are in the post-ARR quests and the post-HW leadup to SB, i.e. not in the bloody expansion itself.
What's worse is that I know SE is capable of handling such a plot,geopolitical intrigue with a side of magical lore is what FF12 was and while the 'editorial' decision to change the protagonist in that game was definitely a very bad call it still manages to work everything else in just fine.
XIV just has a lot of wasted potential in terms of 'plot', SB just happens to be one of the biggest offenders next to Endwalker, EW possibly being worse but having the benefit of being the latest expansion and too filled with fanservice for it to get any real critiques from the typical XIV plot enjoyer.