Here's an GIF of me on the Minecraft preview skin on the new launcher. (Click on the link if ou don't know what I am talking about), you can clearly see that my arms are not glitch. You see on the glove? There's no orange mark on the hand like I show on the second image I show.
And yes, I am using an Alex Model :
So don't take me like I am dumb, we can clearly see just here, I select the model and what he highlight on the timeline? Alex, which is the model of the player who has 3 pixels on his arm.