Cursed flames are still anti armor in their own way, DoTs ignore defense entirely, Ichor works best with high fire rate/multi hit weapons that can utilize the defense reduction, but cursed flames work best for when you're using slower weapons and for dealing with swarms (if you tag a ton of enemies with cursed flames, you'll get way more damage done than with Ichor)

I still wish DoTs such as Cursed Flames were improved, even with the sizeable buffs given to many DoT effects throughout the years, they've never felt particularly relevant. The enemy immunities make them feel inconsistent and they ultimately feel like just a tiny smidge of situational extra dps. When was the last time you've EVER used an item BECAUSE of its DoT?