The story was well written and fun to experience, Emet's involvement with your party and story gives much needed depth to the Ascians...overwhelmingly so, the concept of light and dark's stasis vs progress is very interesting.
Does that mean that Hydaelyn is an agent of progress and Zodiark is the agent of stasis? That would make a bit of sense if the Ascians just wanted to maintain their perfect status quo. So in the First light (=dark/stasis) and dark (=light/progress) are concepts that are flipped?
These beings as Primals is also very interesting, going through the story I thought the implications were massive. What if the entirety of the game was not our own will but only due to tempering? We never refuse or back down from the darkness because we can't? Though ultimately it seems like you just wanna fight to save people and help out, so it never seems so nefarious and when Rocl suggests her tempering is merely "hear think feel" then basically it's a lot less sinister than I thought.
The Ascian disease I have no doubt we'll get more into, but I definitely was intrigued by the whole thing and wanted so much more. If they can make an actual city like Amourot I'll be impressed.
As for the "warrior of darkness" I knew that was a red herring when they basically said the first's concept of light and dark are flipped, they're essentially still calling you the warrior of light, though I suppose now they could rename you the warrior of progress. There was no way you were suddenly going to become dark without a good reason, but I think there's still time to have light vs light with upcoming patches.
As for the resolution to your light problem, I always understood it as Ardbert carrying some of the burden and helping you master the new amount of light you have (now level 80!), when you manage to form the axe you've basically mastered a stronger form of light because your vessel got a lot stronger too. It just seemed like because you were forced to wield the light against the darkness, you just got good at it. It's probably 50% I used it and 50% I got better at it.