S Pen is not the only point here, I think. Note 7 has beautiful & gorgeous display (much better than OP3), better & faster camera, better battery, water & dust resistant, and of course, a memory card slot. So that extra price for Note 7 is for all the above points. The S Pen for Note series, in general, is not only for drawing & sketching, if that is what you are thinking. It also has other useful advantages over other smartphones:
You can practically use the S Pen as a mouse for your device, which comes in handy for a lot of scenarios - quickly sharing a particular content present on the screen, writing on the screen (Image write feature) to better convey & share with others what you really mean to say, multiple selections of photos / files, jotting down anything important quickly when you don't have a notebook with you, signing documents easily on the go, extracting a part of text (it's extremely precise with S Pen) & of course, drawing & sketching, just like you would do on a normal paper, if you like to.
P.S.: You can use your Note 7 with S Pen even when your hands are wet or the display is wet or if it is raining heavily & you really need to use your phone without compromising the touch response of the display, which is almost impossible with other phones, as they do not have a S Pen