I would put a somewhat more positive spin on this. I followed Southland from NBC through TNT, and I think it held up very well, and finished its 5th season at as high a level as most of its fans could reasonable have expected it to. The John Cooper character was as interesting and complex a cop as has appeared on most television programs, all the way to the end, and Lydia Adams, while not quite as original, was still well worth watching. I thought the show was always most pedestrian, and seemed to never really figure out what it was doing, with the Sammy character.
Five years was a good run, all things considered, and I am very appreciative TNT stepped up.