Yes, the story is certainly an over-simplification. Probably doesn't even belong here because this thread is more about Diablo 4 and not the drama.
I don't really want to argue much about the scope and ferocity of the backlash, because it's clear you've seen a lot more negative or disgusting things being written or said than I have. It sucks that that stuff is out there, because it definitely makes it harder to have rational conversations when extreme opinions darken the discourse. I think there's a lot of false conflation between people who are upset about their favorite franchise, and people who are using this as a excuse to throw tantrums and espouse hate, etc. When people rightfully call out those throwing tantrums, sometimes they antagonize those who are viewed on the "same side."
But to respond to your reality question, I assume the press release you mention is the "Diablo at Blizzcon 2018" blog post. It's a post telling people to temper expectations, but it doesn't explicitly mention D4 isn't being announced. Obviously reading between the lines we can infer that, but it still leaves a lot of room for fans to expect *something*. Even the the blog post written to tell people to reduce hype still tells people to stay hyped. As an aside, it's pretty bizarre to have the Blizzard marketing team attempt to reduce hype.
I believe the crux of the issue is the relationship between Blizzard and it's fanbase. It's not about instant Diablo 4 gratification or a mobile game (Although for some, it might be.) There is a lot of evidence that Blizzard abused that relationship. Sure, this is an asymmetrical relationship, but's folly to think that Blizzard owes nothing to the die-hard fans who have supported them all these years.
You've written a few things that would indicate you're optimistic about Diablo 4 and Blizzard, but I think there's a lot of people who have become more pessimistic. Personally, when I saw that Diablo Immortal was developed by a third-party company, I wondered, "How will the famous Blizzard polish be applied?" When I read about NetEase's reputation as a microtransaction factory, I thought about Loot Boxes, Card Packs, and the Real-Money Auction House, and wondered when a pattern becomes a trend. When the only *something* that became of the "Diablo at Blizzcon 2018" was an outsourced mobile game, I thought about the slow death of Diablo 3 and it's near-complete abandonment, I think what was the team working on? And then there's a new rumor that D4 has been rebooted internally, and I think that all of these things I've mentioned means that there's a lot of things going wrong at Blizzard.
Sure, Diablo 4 will come out some day, but can I trust it will have that Blizzard Polish? Will I need to become a whale to enjoy it? Will Blizzard continue to support it so people can still enjoy it after 1000s of hours of gameplay? Those questions used to be easy to answer for Blizzard games. Now a lot of people are not so sure.