Most of these "problems" with email seem to arise from problems with the big online mail "clients", like gmail. I didn't notice Thunderbird in their list of email clients (I use Thunderbird).

I deplore HTML-formatted email anyway. The last time I had to generate HTML-formatted email, the main problem MUA was Microsoft Outlook; I didn't realize that the problem was that Outlook used Microsoft Word's HTML renderer (TIL). I've always hated HTML-formatted email anyway, so jumping through the various hoops to generate HTML email automatically was a real drag.

The article's focus on the wonders of AMP as a solution is scary. AMP is a Google-controlled technology, widely-despised. Making AMP the solution to HTML email looks like a way of tightening Goo's already-tight grip on email's throat.

[Edit] So now a properly-constructed HTML email becomes a multipart with a minimum of three parts: text/plain, HTML and AMP. I don't see this as a wonderful new world.