GIFs historically were pretty unoptimized from a display perspective (as anyone with a moderately-active Tumblr dashboard could tell you), so I wouldn't be surprised if it was worse.
Likewise, for a tiny animation, having the frames of the GIF in memory and blitting them onto the screen in sequence sounds like orders of magnitude less CPU/GPU than performing all the ridiculous math-based transforms over and over again.
The Tumblr example is not instructive here because those were frequently many many frames, very colorful (often photos), and/or large in dimensions, taking up a ton of memory which was probably the main problem causing our browsers to choke. This would be none of those things.