The UI editor should support scaling while keeping the aspect ratio / center of the element the same, by i.e. holding down Shift/Ctrl while resizing respectively.
As someone that doesn’t typically create GUI, I’m using the built-in GUI tool to help map out what I want before making a finalized version. However, I think having scaling tools similar to that of building would be quite helpful. Similar to the basic scaling tools for parts, upon pressing Ctrl or Shift while the object is selected and being scaled will cause it to scale proportionally or maintaining its center position. Shift keeps the aspect ratio and Ctrl would scale the opposite side accordingly.
If Roblox is able to address this issue, it would improve my development experience because I would have a tool to get my UI creation/modification tasks done quicker and more efficiently, similar to the respective tools that are already available for scaling Parts.