Outside of having significantly more formats and methods available (some of which are experimental), the only other thing really notable is that 7zip doesn't seem to have a "tar before" option, like PeaZip does. I can see that in the manual, that 7zip can tar files before compressing but you have to do that manually.

I should probably mention that my original comment was comparing PeaZIp to WinRAR. I actually didn't use 7zip until I tested for the purpose of comparing it to PeaZip in this comment.