Pretty thorough breakdown, and I'd agree with most of it. Some paraphrased bullet points though:

Perhaps stealth isn't doing well right now because of all of those bad stealth sequences in non-stealth games that are otherwise great

Possible, but I doubt it. The late 90s and early 00s was full of those too, but that was also simultaneously the height of stealth games. I think it's just that fads come in waves. Underground racing games were hot when The Fast and the Furious started. World War II shooters were popular after Saving Private Ryan, and modern military shooters followed when a lot of the target demographic either fought in the war on terror or knew someone who did. Dungeons & Dragons and a lot of Led Zeppelin's catalogue only exist because The Lord of the Rings books made a huge impression on people. If something in the cultural zeitgeist comes along that would make a good stealth game, there will be more stealth games; at this point, the last James Bond movie was 5 years ago, and the next one won't be for a while still.

A good compromise we landed on rather than perfect wallhack vision was to mark targets

Perhaps, but I'm even kind of sick of that, too. I played a good portion of MGSV without tagging and found it perfectly playable, largely because, as he acknowledges in the video, you can scope it out from any angle from far away before you make your approach. This is something the original Deus Ex and Ghost Recon: Wildlands do well too, even though the latter also does the trivialized target marking. I don't mind some light wallhacks when you're up close to simulate the character's hearing, like in The Last of Us. If we found ourselves in that stealth situation in real life, we'd have pretty good three-dimensional awareness of enemy locations just by the way sound bounces off the walls, and I think it's okay to represent that in some way. I think the marking target mechanic is so prevalent because Ubisoft made a large number of games featured in this video and inspired more still; and Ubisoft for the last decade and change has been a company that made an efficient machine for churning out games that used a lot of common mechanics between multiple franchises.

Playing through 007 First Light right now, a lot of my most common grievances are in predictability, but not of the enemies. There are a lot of context-sensitive actions, and while this game has a sort of tutorial that we'll be talking about for years, it did a poor job of explaining those contexts to me. I had similar issues blackjacking guards in Thief, and there's that guy-on-the-couch section in Splinter Cell that he highlights in the save scumming section that you could describe much the same.