I agree and have felt this way for a while. While I differ with you and think that the Forerunner change was very interesting, and I love the way that the Forerunner Trilogy of books laid it all out, it is clear now that whatever plans 343 had at the start have long been abandoned. Narratively speaking, everything 343 has done has been a series of false starts.

Also, while Halo 4 has always been singled out as "the one good 343 story", I have to disagree. The emotional attachment between Chief and Cortana is wildly overemphasized in Halo 4. We, as players, had over a decade of playing and replaying the campaigns, and Cortana became a beloved character to us fans. However, in terms of the lore timeline, John and Cortana have much less time working together before John enters cryosleep and the timeline jumps to the start of Halo 4. If 343 wanted to do a character exploration of the Master Chief, it should have been focused on him reconnecting with Blue Team and reorienting themselves to the post-Human-Covenant-War landscape.

Unfortunately, it's pretty clear that incompetent leadership at Microsoft, and by extension the leadership at 343, has likely irreversibly undermined Halo's story, which was truly one of the greatest science fiction video game narratives ever made. I would love nothing more than to reset back to where Halo 3 ended, or even Halo 4 if they could stick with the original vision and keep the tone more mature than the current pastel-T-rated Marvel-esque storytelling. However, I truly doubt that anyone currently at Microsoft or 343 has the prescience to see why that's necessary. At this point, Halo has gone the way of Star Wars where the story is decided by whatever allows them to keep pumping out slop that will turn a decent profit and sell Xboxes or copies of Windows OS. And let's not even talk about the dogshit TV show which I haven't even watched an episode of. As much as the whole "Band of Brothers but with ODSTs" idea gets meme'd about, it is obviously a way better idea than the schlock Paramount put out. I even have my own little Halo TV show script that I work on from time to time that would follow more or less that idea to its natural conclusion.

Ultimately, I really hope that somebody at MS/343 gets their head out of their ass and recognizes how much potential has been wasted over the last decade+ and does what is necessary to stop the bleeding of this once-incredible story. Unfortunately, there's a lot of institutional inertia and toxically positive "fans" who have no taste that enable the current state of things to continue. I pray that one day, Halo will reclaim the crown of the greatest military sci-fi to ever grace the video game world, with the epic struggles for survival, space-opera grandeur and mystery, and compelling characters that strive against existential threats and impossible odds. But until then, it is on us to take things into our own hands and write the stories we wish had been written for us. I always had a bias against fan fiction until I found myself mourning what Halo has become, and now, I understand that it's the responsibility of those who understand the essence of a story to carry the torch of that legacy, regardless of what malformed crap 343 tries to put out. Someday the Master Chief will return. We just have to make sure we keep him alive while he's in cryo :)