Again standard content is standard content. You wont keep a lot of the casual players playing if you only have a couple of dungeons, trials and the two raids. They are nice, they are necessary but they are also done fast. Which is already a problem with each new patch because people are often finishing it fast and if you are not a raider or like Eureka (which as you said is only for a niche anyway) then you have nothing else to grind for thus nothing else to sub for.
You are right PVP is a huge thing but honestly still niche (and kinda a bit dead for quite some maps) and not that isolated like Eureka. You can level up your characters there (which was probably a change done to get more people to play it) and work towards some rewards but in the end its still niche content.
About more huge content for players with less time: Because like PotD even if you dont have much time you can work towards your goal slowly, without having to grind it hardcore at the start of a patch and still get something out of it all the time. Also because the standard content we have dont hold up for long. If you dont want to grind if for some glamours you might just do your dailies and be done with that content. So what now? Here it would be perfect to have casual content that you can do on your own time.
The only thing where I talked about the relic was a few pages back when someone said that we are never happy as customers and when someone used Eureka numbers to make a point about it. Otherwise I am talking about battle content itself which Eureka is, but as numbers show and as Reynhard tries to say, its somehow niche content thus not for the casual players.
In HW we got new battle content, it was called PoTD and then we got two versions of Diadem. Sadly both Diadems failed but they were still quite casual content. The only thing that is truly new in SB is Eureka which, if we can Yoshidas quote for real, was always meant to just be something niche. So where is the true casual battle content?