If that is the worst, it's not serious. I agree with the sentiment here. The pinch weld is two pieces of metal. I see the outer piece has pitting/holes, if the inner is ok, it will act as a backer for some MIG fill and grind smooth. As said, the area will be covered. Weld is the best way to fix rust if you are experienced, if not, the other ways mentioned will probably last awhile.
Now for the bad news. You have shown us a picture of an area that has thick paint or epoxy. This is covering a possible can of worms. I would remove all coating all around and see what you have. We can't really advise until the whole picture is exposed. You don't even know how bad that one area is yet.
