People tend to use the word "content" to describe gameplay rather than rewards. But even for the people who do use the word "content" to describe rewards, complaints about RNG aren't a complaint about content, they're a complaint how the designers chose to implement content.
Take paragon chests as an example. The developer has some rewards already designed and ready to be implemented, whether toy or mount. They want to connect it to paragon chests you earn from continuing to grind rep after hitting exalted. They could choose to:
A) Add a currency connected to paragon chests, and set the prices in line with what they judge to be a reasonable time-frame. This also gives players the benefit of being able to assess the time vs. reward directly.
B) Set it to an RNG fractional rate with a bad luck protection system in place - for instance, you could randomly get it from your first chest on upwards, but if you hit 20 chests (200,000k rep grinded past exalted) the system makes the drop guaranteed.
C) Set it to an RNG fractional rate, with no bad luck protection in place - an unlucky player pursuing this item may never get it, or might only get it long after the expansion is over (for instance, you hear of people who grinded paragon chests throughout Legion, never got their mount, and are STILL grinding Legion faction rep).
Is a complaint if they choose "Option C" a complaint about "too much content," or is it a complaint that the developer is making crappy decisions with the assets the designers hand him? What if they take a big chunk of rewards, say over a hundred, and throw all of it into the "Option C" bin. A lot of complaints may sound like, "there's too much" on the surface, but if the developer spends a minute looking one inch below the surface, what they'll find is a dislike of how they're implementing rewards, not that they have too many rewards to implement.
Edit: I will admit, I've done PvP island expeditions lately, and enjoyed them a lot more than PvE island expeditions. And I'll give credit to Blizzard for improving the gameplay of island expeditions in general above what it was at launch. I still think the reward side is badly mishandled though.