Maximally optimizing image loading for the web in 2021

Malte Ubl’s list for:

8 image loading optimization techniques to minimize both the bandwidth used for loading images on the web and the CPU usage for image display.

Fluid width images in CSS, not forgetting the height and width attributes in HTML so you get proper aspect-ratio on first render.
Use content-visibility: auto;
Send AVIF when you can.
Use responsive images syntax.
Set far-out expires headers on images and have a cache-busting strategy (like changing the file name).
Use loading="lazy"
Use decoding="async"
Use inline CSS/SVG for a blurry placeholder.

Apparently, there is but one tool that does it all: eleventy-high-performance-blog.

My thoughts:

If you are lazy loading, do you really need to do the content-visibilty thing also? They seem very related.
Serving AVIF is usually good, but it seems less cut-and-dry than WebP was. You need to make sure your AVIF version is both better and smaller, which feels like a manual process right now. Update: I’m told that AVIF is actually more-reliably smaller (than JPG at least) than WebP is on the whole. I still think it’s worth being careful. This makes me want to outsource format choice to cloud providers that serve in the smallest format they can produce even moreso.
The decoding thing seems weird. I’ll totally use it if it’s a free perf win, but if it’s always a good idea, shouldn’t the browser just always do it?
I’m not super convinced blurry placeholders are in the same category of necessary as the rest of this stuff. Feels like a trend.