I'm a bit of a unix noob, but this question seems super basic, yet I can't find an answer anywhere.

Basically, to my knowledge, sFTP is just FTP over ssh. So, why can't I drag and drop files from one folder to another on the server side like I can on ssh. Why when I want to unzip a .tar in a server folder, does it first want to copy it to my machine and then back? Why can't it just unzip like it can when I'm using the command line. I know that when I use the command line it is using the resources of the remote machine, but why can't sFTP do that too?

Is there a way to execute commands which I would normally do over SSH, but in a gui? I'm tried mapping to the drive to my own machine, I've tried so many sFTP clients that it's silly. Is there another class of program that I just don't know of?