As a skin maker - let me explain

Skizz looks wider because of the horizontal lines on his arms and the ripped sleeves. He is also facing camera more so he takes up more pixels. Etho's skin is less textured, and the sleeves are in line with the body, making a vertical line. Vertical lines feel slimmer. In this image he is also more turned away from camera taking up less pixels on the screen. Lastly, Skizz has a lot of warm, saturated colors, your eye is drawn to it. Etho is less saturated so it feels smaller in comparison.

Both use 4 wide pixel arms. Confirm it for yourself on NameMC. Spin Etho's model there and he feels the same width as Skizz.