If the first movie was Flynn vs. Dillinger, and the second one was Flynns vs. their own creations, then it makes sense that the third would be Dillingers vs. their own creations, and then a final film for the final Flynn vs. Dillinger, which is what was set up but probably won't ever happen. I do agree that Ares is the weakest of the three, but I can see where it logically fits in, as long as there's the fourth and final part.