Vanilla animation swings arms and legs a lot and it looks quite weird in my opinion. It would be really nice if there was a proper gliding animation.

But there is a proper animation, currently there is just issue tr7zw/FirstPersonModel#96 with the FirstPersonMod that the PaperDoll does move arms/legs when gliding, while in f5 you in fact don't do that.

Interesting. It must be a mod conflict on my end then. I will post here again after further testing. My suspicion is customizable elytras or curios elytra mod. Every other animation works but when flying with elytra it moves arms and legs as if running extremely fast, weird.

I am closing this issue until I find what is causing this problem.

Huh odd. It might get something wrong to place the wrong animations(I also have/had a lot of fun with the elytra animation in the paper doll as you can see with the issue above).

Is this problem manageable on your end (like overriding it, I don't know) or should I open an issue on their github?

It turns out to be an issue if this mod is used with Abnormals Personality mod , which adds few animations too. But I am not sure why it causes a problem with elytra flying as it only adds crawling, sitting and stair climbing animations as far as I know.