I think the surprising thing is that JPEG is as good as it is. WebP certainly isn't "1/2 of the current size at the same quality and decode speed". It's a modest improvement if anything.
GIF, sure. But, IMO, nobody should really be using GIFs anymore. We've had <video> and APNG for a while if you want animation.
The speed modern web concerns me. The standards are not moving forward. We still use HTML, CSS, Javascript, Jpeg, Gif, and PNG. Gif especially is a format where we could see similar sized/quality moving images at 1/8th the file size if we supported algorithms similar to those found in modern video.
In all of these cases, they aren't "tried and true" so much as "we've had so many problems with each that we've got a huge suite of half-hacked solutions to pretty much everything you could want to do". We haven't moved forward because we can't. WebP is a good example of a superior format that never stood a chance because front-end web technology is not flexible.