In my last font manager, I could right click on any font and if I selected the option of adding it to a group, I could select the group I wanted from a list. This is much more convenient than dragging and dropping, particularly if you want to assign the same font to multiple groups.
This would be a nice feature. : )
You can also use the familiar shortcuts for Copy and Paste (Ctrl C, Ctrl V) to copy fonts to several different groups. Copy once, e.g. from the Recently Added fonts view, then paste them to many different groups. That is faster than right-click to view a context menu, then scrolling down through a long list of groups to find the right one (depending on how many groups you have).