1. Shiva unreal is not casual content, neither is the new extreme
2. Just because relics didn't bring unique content doesn't mean that it wasn't fun or at the very least kept people coming back. I point you to Yokai as an example; people don't "like" fates, but in reality they do, mainly because it's accessible (casual) and brings friends/community together, essentially the same reason people engaged eureka (and potentially Bozja).
Again, the problem with the game is they prioritize the savage crowd at the start of the patches and then throw a bone at the casuals at the end of patches. Casuals have less patience, it's why you always see a sharp decline in subs, duty roulette every day won't keep them around for long.