I too am a bit surprised this made it on the front page. Mu4e is definitely niche, and I wouldn't crow about it like I do org or magit. I've only been using it for less than a month and it will be a while before I know whether it is a net win.
Also, the real test would have been my much more voluminous work email!
The HTML rendering isn't great, as you said, but you are two keystrokes from opening that email in a browser, if you have to.
And I have tweaked the config several times now, but I think that's mostly because I'm changing my (and the charity's) email, which involves a lot of shuffling about. Again, in six months, I'll have another look and decide whether it _really_ helped.
This was my second attempt to get email working on Emacs and I gave up the first time, too. I persisted this time and I _think_ it will pay off. There is the obvious danger of this becoming another "project", but I'll make a note to check-in again in six months. It's an experiment!
I've not seen the other things you mentioned. I only check for email every 10 minutes, but opening and (especially) searching for emails seem much faster than doing it in Gmail. Plus, I can do searches across email accounts, like all unreads across all three accounts. That was definitely slower in the online clients.
Finally, there's a quick ('a' then 'v') way to just open a message in a browser if the HTML is too thick.
This is an important point that I missed and didn't mention: My work and school life were really hard and chaotic. This is so intrinsically part of me that I didn't even notice, but has generated a lot of stress on me and my family. I guess getting treatment would have saved me a lot of that. I wonder if it is worth it, as a 62-year-old and probably within 5/6-ish years of retirement?
I worry about all of this labelling that we apply to various ends of the "normal" spectrum. Where does it lead us? Is it actually helping?
I easily score as ADHD, but I'm in my 60s now and have never been diagnosed or treated. I have muddled through all my life. Yes, I often self-medicated unhealthily (cigarettes, various over-the-counter uppers), but also relatively healthily (I've been practicing meditation for decades). I managed to have two, long, fruitful careers (20 years of journalism, coming up to 20 years of software engineering) that (I'm betting) was at least partly attributable to me being on the outer edges of normal.
I think that's OK. I'm not looking to be "treated" because I'm a bit different.
I love these packages (like this, Spacemacs, Doom, etc.), even though I've used Emacs for over 30 years. I don't use them directly, but they give me ideas and alert me to packages I haven't heard of (eat?). And that gives me an excuse to go on another round of config-tweaking, which any Emacs user loves.