The closest thing I found was this, but it still is only a PNG so the compression size will be different. Though this would be good for comparing textures I guess. But also, a texture may look bad on it’s 2D representation, but may look good on the model, and vice versa. The UV mapping and lighting can play a big role in how good a texture looks.
What I was thinking was an editor script that can automatically scale the textures, check their sizes, take a screenshot of the avatar with it (like this?), and then compile or export a report of sorts so there is no guesswork involved.
But I guess the hard part would be to check bundle sizes since it needs to go through the entire process of building for upload. This may at least help for testing textures, maybe, but even then, people can use Thry’s Avatar Performance tool to check VRAM sizes and go through each texture, reducing their quality until it is on the border of visually acceptable.