Dealing with widespread surface damage is a real pain, especially when you don't have a clear record of how it happened. Most of these kinds of scratches are in the clear coat, which is good because that's what protects the paint underneath. You don't necessarily need a full repaint to fix it, but you do need the right process.
Start by getting the area really clean, removing any grit that might just scratch it worse during polishing. Then, you're going to need a quality cutting compound and some microfiber pads. Applying it in small sections and using circular motions should gradually raise the paint level enough to minimize those lines. It takes patience, because these deep scrapes require several passes, starting with a more aggressive polish and finishing with a finer one. Once you've corrected the deepest marks, finish the whole area with a quality wax or sealant. That layer acts as a sacrificial barrier, protecting the repair from future incidents and making the whole thing look uniform. This method can significantly improve appearance without the huge cost of a professional body shop job.