Swapping in the DLC kind of helps.
I'm currently doing a 2nd playthrough of the Royal Edition on Xbox One X now that the game is done. I wish the DLC could be more cleanly integrated then me quitting into the menu when I feel it's appropriate, but whatever. Still it works and his filled in some of the story. I did the Gladio DLC when he came back to the party and it fit in well. Stop at a campsite on your way back to Camp Caem in chapter 8 for extra immersion! Then did Ignis after chapter 10 which I think is a good idea. Sure it shows glimpses of the ending which will probably not really spoil those who are playing for the first time, but the epilogue dosen't fit cleanly if you want this to all to flow correctly. Still, the events of the Ignis DLC help understand the 2nd half of the game.
I think the Ardyn dlc should be played right after the chapter where Noctis goes into the crystal and Ardyn reveals his name. Seems like it will make most sense there. Especially when dialogue already in the game refers to those events. Not sure where I'll swamp in Prompto. But still the extra additions are improving the game. It will never be a tightly woven package(maybe a PS5 type re-release will do this), but still I will say my opinion is improving.