I own a body shop and we know how to do good work.
More, better pics will help, but it looks like the metal is ripped ... so it will have to be welded anyway. While it can be saved with the right amount of time and attention, a replacement panel looks like it will be the better option. Beating the metal out will stretch it. Also, no matter how well the outside of the car is fixed using a combination of metal work and body filler, when looking at the metal from the inside of the trunk, it will show its scars. With a replacement panel, only as much as needed can be used, much of the factory seam welds can be used for a factory cut, and the areas where a make-shift welded cut is done can be grinded flat making the inside look much more tidy.
Fixing the original metal is not easier than replacing the panel. The outcome will not be better either. Depending on how bad the panel is, you will possibly have to cut the metal out anyway to straighten it so it can then be reattached, which is the same process you would go through to replace the panel minus the metal straightening. The only thing that would stop me from replacing the panel is the availability of a replacement panel.
While many will have opinions, you should rely on the opinions of professionals you trust who inspect the vehicle up close.