I don't buy that uutils will be a meaningful improvement for security. Though replacing GPL licensed coreutils with a MIT licensed alternative is not a good look for Ubuntu's support of free software.
It could be argued that it's not a good look for Ubuntu's support of copyleft, but MIT license _is_ free software, as per the FSF definition of free software.
Why? Because it hasn't been a consistent major vector for attack in the last couple of decades?