Among the many problems with ARR content is enemy HP being too low, breaking fights like Cape Westwind, CM, Prae, Lab, ST where you skip most of the mechanics. Most people joining the game after 2014 never got to see the full version of these fights and the story bosses come across like a big joke in battle compared to the way the story presents them as formidable adversaries. None of the expansions have fights that are broken that badly by item level increasing in patches.

I sure wish they could remake some of the ARR instanced content using everything they've learned since then about battle design. The ways I'd justify time being spent on ARR remakes is [1] it doesn't really divert resources from new content because those old fights would essentially become new content again, you can put in mechanics to surprise old players and add new item rewards to make them relevant (song rolls, minions, lv50 glamour) and [2] improving the base game would leave a better impression on new players who must pass through that stuff before they can see the better designed stuff in the expansions.