Sure. I'll go to details over it why the narrative isn't as strong as what you proclaimed it to be.
The entire first generation is a deconstruction of the typical Fire Emblem "war is the solution to everything" plot through the lens of "what would happen if a young adult who had no political experience outside of being a soldier came to power?". The fact that Sigurd's only answer to any sort of dissent is to conquer the opposing party slowly drives the entirety of Agustria away from him (including his former friend Eldigan), grants Grannvale the power it needs to slowly turn tyrannical, destabilizes Sileese by being the final push for the state to enter a secession war, and allows Freege, Dozel, and Velthomer to make things even worse by installing themselves as oppressive, colonial governments in his conquered territories.
War literally
is the only way in which seliph and leif (aka the good guys) wins back power (it is part of the overall story, and cannot be separated from the overall narrative). The story did force sigurd into bad positions despite him doing decent-ish stuff to help the region after the first war, and it was a series of bad events, external issues (e.g. Arvis) and being too trusting (you know, the kind of thing people rip corrin/eirika/micaiah for being too "naive" for) outside of his hands that resulted in the following disaster, not necessarily the actions that he took up.
Showing a flow of such a story means nothing when there's no growth to said character, and a deconstruction for the sake of doing so is not strong storytelling by itself (GOT deconstruction for the sake of doing so is a very clear example). Especially when it's clear people were saved when sigurd took action while certain states were already in conflict before he stepped in, that's not a strong statement on the "deconstruction" you stated it to be.
Also, why would Arvis get rid of the nobility power structure? He's a man driven purely by his own self-interest and the goddamn emperor of the continent's superpower that is only growing in influence. Why would he surrender his power through grand reforms out of a sense of personal morality when it's clear he primarily looks out for number one? Plus, he does introduce reform when it benefits him, as seen by his willingness to reintroduce the Loptr Church and its people to re-enter society without fear of being lynched. Likewise, Seliph only becomes emperor in the final cutscene of the game and his story is based around uncovering Julia's past and learning to live up to the massive legacy he's inherited. It's fine that the game doesn't really go into what Seliph is like as a political leader, because for 99% of the game he has no political power.
So we do agree that Arvis was a terrible person and that his "justification" was nothing more than just a hunger for power. That doesn't strike me as an interesting or complex antagonist other than the fact that he killed the protagonist (you could make a case for cunning, but that just means he's a rat monster, not some sadman who set some people on fire).
Also your point about "reintroducing the Loptr Church" worked really well when
literal satan aka manfroy was working behind his back to revive said evil world-ending monster (who enslaved the entire continent for centuries, how do you even try to spin it as a sympathetic thing). Nothing about the plot indicated that giving them a chance resulted in anything good (which again, shoots down the argument that the plot was trying to show complexity through it).
And given how many of the continent's problems and issues were implicitly indicated to be linked to the nobility and the bloodline obsession causing a lot of problems (corruption, war, genocide and a young adult being thrust into making the world's best decisions as you said), then reinforcing the same power structure through emperor seliph does mean that the root issues were never addressed directly, no? Especially when bad things can easily happen again in the future after seliph passes on? Or that the game vaguely makes a point about it and never addresses it at the end of the game?
Just because they're not waxing philosophical every 5 minutes about their ideology like Edelgard doesn't mean that Arvis and Seliph aren't well-written or interesting characters.
I don't disagree that fe4 has some well written characters, but this is no different compared to other FE games where you get some well written characters, some bad and some creepy. Why does it make the game more different/better compared to others, especially as a 10/10 game?
Also, just because a theme has been already covered in a pre-existing work doesn't mean it automatically invalidates the new work. The Loptr are much more interesting than the other unambiguously bad FE factions like the Earth Dragons and Those That Slither in the Dark because they have some degree of reasonable motivation to do what they do. They were cast permanently into hiding out of a fear that they will be lynched for their heritage. It's no wonder they want political power and follow an extreme religion, they are at the bottom rung of society by virtually every metric.
Of course! It's just funny because the Loptr had.....Manfroy and his ilk who were literally the cartoon villains in the story (you know, the whole deal about reviving evil world ending dragon without any subtlety to it). The game never really bothered to point out how bad it went for the tribe (saying it doesn't make it compelling btw) and the fact they went on to do bad things without giving 2 hoots (haha child hunts and mass murder; so much for trusting in them huh?) and the fact that the ending never addresses the things that happens to the Loptr people (who were not angels btw), makes me think the plot point was never handled well. Honestly that's FE4 in a nutshell - interesting points that never gets addressed directly or ever developed properly.
I do find it interesting that you raised the former while not addressing the other kinds of antagonists like Mila/Duma, Black Knight, Lyon and even edelgard. Surely characters with differing motivations and personalities are more interesting to you than....the unambiguous bad factions you pointed out?
Likewise, while Loptous is very much just an "evil for evil's sake" character, even he's more interesting than the likes of Medeus simply because there's a tragedy behind him. Julius is permanently corrupted by the tome and undergoes a major personality change, which leads to characters like Ishtar and Arvis tragically continuing to follow him out of a sense that he may return to his old self.
Great to see you agree that Loptous was pure evil! So here's the thing - how is that more compelling then the other "big bad wasn't so bad" that is repeated in the past/future games, like hardin, lyon with good intentions failing and turning to the dark side, or the yune/ashera dichotomy and sephiran? I don't think the stated examples are without fail of course, but since you were the one who stated FE4 was superior in all that i would like to know more about how you came to that conclusion.
Heck, we literally see the same plot points repeated with Xander and Garon, and we all know fans viewed Xander as an idiot for bowing to his father (even through he was clearly subordinate to his father, something that Arvis cannot take solace in - you're the goddam father, do something about your genocidal son, just because the previous emperor told you to pass the mantle down does not mean the son can do whatever he wants, its not realistic).
It's not like Julius was shown to be some deep compelling fleshed out character before he was posessed where we, as the player, would understand and feel sad that Ishtar would do this? "Show don't tell" is so important for these types of stories and it's clearly not done well here.
My issues with FE4 goes deeper than that of course (i don't feel like this is the right place to really dig into those; but i'm always happy to elaborate further if need be).
That said, it's not a bad game either. Interesting big maps! Good revenge story where the son avenges his family! Interesting characters!
But these does not strike me as a
10/10 game like you stated - especially when i've pointed out the other FE games also go through the same kind of points you mentioned too. At the end of the day, it's.... just another FE game. Some good points, some bad points, some what-were-they-thinking ideas all thrown in. Nothing wrong with that, no?