Demacia is my favorite faction in the lore, and I want them to be in a healthy state, but as-is... They're too one-dimensional. There's no polite way to say this: Demacia's not working as a faction right now. People do not see them as morally gray, they're seeing them as evil with a veneer of good.
Now, to Riot's credit, Sylas is NOT a bad character and the idea of a revolution in Demacia for the mages is not a bad one to explore. We had some hints earlier with Jarvan/Shyvana that the former was working to make Demacia less intolerant of magic, but was doing so within Demacia's system. The idea of an extremist who wants the crown brought down NOW is a natural place to go from all of the talk of Demacia's authoritarianism and heavy anti-magic stance (it contrasts nicely with Jarvan's more measured approach with Shyvana)
The big issue is that we're ONLY seeing Demacia through its anti-magic lense. Noxus, we see its brutality but also its heavy sense of meritocracy. Taliyah's story showcases both pretty quickly and effectively: she's brought along to Ionia to fight for Noxus' cause. This is something most other factions in the lore would not do, despite how useful her powers would be; Piltover and Noxus are too focused on magitech, the Freljord is very insular, Demacia outright hates magic... hell, Ionia only got involved in teaching her how to use her powers, not in the actual fight. But when Taliyah said she would NOT fight, the Noxians she was with tried to kill her. That's their big pro (merit and individualism) versus their big con (brutality and warmongering).
When you look at the various factions of Runeterra and their regions, you see this kind of thing all over the place. Ionia has proud, wise traditions and is fighting an oppressive invader, but their traditions are inflexible and their fight is arguably destroying what it means to be Ionian in the process. The Vastaya (exemplified by Xayah and Rakan) are fighting for the freedom and continuation of their people, but do so in a brutal and heartless fashion. Ashe is inspiring the Freljord through the legends of Avarosa, but thinks of herself as a false prophet.
But they key point is that these are not the *only* dimensions to each realm; they are not all viewed through the same conflict. Noxus' brutality and meritocratic nature are seen not just in war; Varus and Vladimir both have stories that talk about Noxian artists while the Principles of Strength shows how Noxus deals in terms of diplomacy. Ionia has Irelia and Karma to represent different ways of dealing with Noxus. They have the Kinkou and Order of Shadows, who have their own angle on not just Noxus but their own place in the world. The Freljord has Sejuani preaching a doctrine of blood and conquest, as well as Ornn showing off their more mystical aspect, and Lissandra's focused on the Void. Targon has the war with the void, battle with one another, Taric turning into the protector of all things, Aurelion Sol rocketing back to Runeterra... You see? Angles on all of their pros and cons, not just the ONE conflict.
For Demacia, their big Pro is supposed to be their unity and togetherness. When someone in Demacia is suffering or in need, their fellows are there to help however they can. Turmoil actually did do this pretty well imo by getting the soldier to talk the townspeople down and for no one to press charges about it (tell me that would've happened if someone had done that to, say, Sejuani or Azir) but the problem is that the central conflict of the piece is still around Demacia's stance on magic. It needs to be emphasized more [i]outside[/i] of the magic vs anti-magic narrative.
Some areas of the lore I thought did this well:
-Turmoil, as said
-Garen's encounter with the Stone Hag. More specifically, I like the bit where he says that he called her the Lady of the Stones because it was rude to call someone a hag in their own home.
-Poppy embodies that whole idea about being there to help your fellows.
-Shyvana's entire lore and color story.
So... do more of that but cut the anti-magic stance. Focus on how Demacia is a place of unity and brotherhood in a situation that has little to nothing to do with magic. Some kind of last stand story, perhaps.