WebM (despite being closely related to WebP) can be 5-10x more efficient than WebP.
That's because WebP focused so strongly on being a GIF equivalent that it also dropped all things that made WebM efficient and instead adopted GIF's awfully inefficient architecture (just dumb frames overlaid on top of each other, without motion vectors or predicted frames).
Safari shows how it can be done: it supports silent MP4/H.264 straight in <img>. You get all the ease of use GIF, order of magnitude smaller file, and hardware acceleration.
It's unintuitive, but well-compressed videos are cheaper to decode than dumb "animation" formats, because file size differences are so massive that it's cheaper to decompress a small amount of complex data than to chew through vast amounts of poorly compressed data.
There's also the practical matter of network speed. In many common scenarios a 300kb webm can be fully downloaded and playing while a roughly equivalent 5mb gif is paused a few frames in, buffering.
I can't imagine any cheap SoC for smartphones without H.264 HW decoder because playing video is essential and it can record video. Possibly exists for low-feature phones without camera but it's not for web browsing.
The licenses for codecs sometimes cut into the thin margins on budget phones. A large amount of people outside of the US and EU are stuck on low-end phones, and I'm pretty sure many of the government subsidized phones in the US are in the same boat.
That's because WebP focused so strongly on being a GIF equivalent that it also dropped all things that made WebM efficient and instead adopted GIF's awfully inefficient architecture (just dumb frames overlaid on top of each other, without motion vectors or predicted frames).
Safari shows how it can be done: it supports silent MP4/H.264 straight in <img>. You get all the ease of use GIF, order of magnitude smaller file, and hardware acceleration.
It's unintuitive, but well-compressed videos are cheaper to decode than dumb "animation" formats, because file size differences are so massive that it's cheaper to decompress a small amount of complex data than to chew through vast amounts of poorly compressed data.