Animation.

Manually deleting the duplicated and unnecessary frames greatly decreases the file's size, and so far in my practicing, shows more accuracy than automatically deleting every second frame.

Of course, that holds a lot more work than simply having the computer do it. Moreover, I notice that your Idle Pose .gifs have a huge number of frames, which I assume is by effect of the 500~1,000 Frame videos (or from being a higher quality[?]); if done manually, "unnecessary" translates to "A few pixels moved that isn't discerning to the human eye".

With that, it's more like x1.3~x1.5~x1.8 rather than x2. If you could show a sample of one of the (unedited) pose video files I would like to see how it is myself to more fully understand.