They've tried many things for the Relics over the years, and some of them have been worse than others...

Personally, I don't mind some grinding being involved, but I want it to be a quantifiable amount of grind. Having a low drop chance for the atmas isn't really grinding, it's just a matter of getting lucky. Specially with the Demiatmas for EW if you do it in Crescent as you also have to hope the game spawns FATEs and CEs in the correct part of the map.
Adding RNG to the grind only makes it artificially longer.

I think HW generally did the Relic the best, aside from earlier on in the expansion where you needed HQ items from Crafters to finish a step... Since not everyone is an omni-crafter or has unlimited gil to spend... But overall, you had multiple things you could do for progress on the Relic, and you had a generally clear measurement on how much grind you had left.