I'm starting to get the feeling that a major missing contributor to this block is the exact reason the first block was successful.
Chiefly, the first Zendikar was a huge expansive world with a mystery. There were obvious problems with the believability of how life got along, and naturally, the mystery was solved, but there was an immense sense of scope that really offered ago much potential.
Flash forward to now and this relatively tiny crowd on whom we are focused. They are so glued to the sea gate plot that the rest of Zendikar is pointless... And that is fatal when the success of the world was predicated on immensity. Their attempts to focus on such a small group has ruined the flavor of the world rather than reinforce the "stand as one" theme they were hoping for.
Add in pointless redesigns like the goblins and kor and you consequently alienate the damn people you're trying to lure back.
Hilariously, I think they over corrected the problems they had with return to ravnica by changing too much while ravnica changed too little.
Where I stand on this is similar. Though it was a different time of Creative direction and Zendikar was the adventure world, few mysteries were even answered. I certainly hope we'll get tons of answers with the lore book, but the time between starting the story and releasing that information is painfully long. It's an intentional gap to keep focus on the Sea Gate storyline, seemingly effective in accomplishing that.
Honestly, if they can get semi-regular UR readers to say "Yes, this conflict is centered around Sea Gate," then I'm fine with how repetitive and singular the conflict is. Limiting it to one location and focusing on a small group of known characters is how newer Vorthos are able to jump into the story without too much research. Just like some sets don't have the depth I'd prefer, some block stories will not be "for me". I'll be upset if this is story depth is a baseline for the future, but that seems unlikely.