This file doesn't really scale with the recommended 135px for wgLogo. I tried previewing https://upload.wikimedia.org/wikipedia/commons/thumb/4/41/Commons-logo-en.svg/135px-Commons-logo-en.svg.png on my browser but it doesn't fit unless the height of #p-logo is increased.
$ curl https://commons.wikimedia.org/wiki/Main_Page 2> /dev/null | grep apple <link rel="apple-touch-icon" href="/static/apple-touch/commons.png" />
Should be filed in a separate task though.
Ah, you're right. Wiki-commons.png does seem to be the right size.
And it is better than what is currently in the corner, even though it is not perfect.
There may be some way to improve sharpness further in the future, but please apply the current wiki-commons.png for now, if possible.
Improvements include symmetry of the inward pointing arrows, incrementally sharper borders on the outside and inside, and crisper colors.
Newly uploaded version: