twentysixteen .site-description CSS seems a bit off

Indeed it does cut it off, I’ve just tested using a default installation.

You can rectify this without it affecting your line-height by using:

.site-branding {
    overflow: inherit;
}

Yes that does a nice job of it. Should I mark this resolved or leave it for the twentysixteen people to sort a bit more?

I did a search of the GitHub repo. It looks like this is already being discussed: https://github.com/WordPress/twentysixteen/issues/454

You can find the proposed fix here: https://github.com/WordPress/twentysixteen/pull/452/files

…but it doesn’t appear to have been merged as a part of an update yet.