He might be making things worse. The new art on the Universe page shows a Demacian city getting wrecked and several Demacian champs being restrained with chains featuring heavily in every image. I'm getting pretty classical magical rampage vibes.
Which is not exactly a great way to make Demacians hate magic less.
So if Sylas is the one going around wrecking bits of Demacia, he's making things worse for mages in the long run.
They're visions, hence why they're listed under "Visions of Demacia." I don't think any of the images released are indicative of how Demacia is now - they're what-ifs in the scenario that the chained champion takes control of some of Demacia's elite and destroys the city using the very magic they use but warp and bend to the laws of the city.
It's most likely something ala Jhin teaser.
It's promotional art. 2019 and people still think promos are lore
Ah yes like how Vi and Sona are now canonically dead because they were shot by Jhin in the teasers ....
its dominatrix 
not a new champ .....
Sylas' gift of magic was that he can see magic in others as brilliant light around that person.
Nothing was said or shown that he could weaponize it nor that this was his intention.
Even he chose to walk away from his duty as a Demacian "mageseeker" (not his official title) after all the massacre he witnessed, knowing full well that eventually they'll seek him out and "bring him to justice" when they find him.
Killing people indiscriminately because they carry the gift of magic, was eventually going to bite Demacians in the ass. Not every mage seeks out to destroy others with the power they have and just as was in the story mentioned already, they decided to "attack" the village over a small plant that was grown by magic and being sold in Demacia presumably.
In any case, my belief is that whoever this mysterious person with the golden chains is, they'll have a score to settle with Demacia for this very reason. Either for them being Demacian captive for years in an anti-magic prison or perhaps losing their loved ones by the hands of the Mageskeekers.
Keep in mind the symbolism of these visions. Demacia being ravaged by the very thing they try to deny in the world. And these are no small feats of magic, these champions were specifically chosen since they represent the light of Demacia in one way or another:
#Imagine if all their powerful gifts and influence were used against them...
Probably lost his shit after he killed his daughter and doesn't really care about forgiving Demacia anymore.
I just hope he's animesque :D
For one art might not portray canon events that happened or will happened but more of a showcasing of the character. Regardless in his lore he could still have taken violent action against Demacia. As for making things worse, Demacia already has a dedicated group that is made for killing mages that are in fact their own flesh and blood. And to a degree it is true that such things seldom change without violence. Regardless of the nuances though, a Demacian mage that is straight up taking the war on them to maybe change his homeland even If through bloodshed is something I have been waiting and it is pretty reasonable that it would eventually occur.
