I think Battlefield should have taken a page out of COD's book (of all things) and broken their series up into subseries.
Like, with COD you can think of there as basically being four rotations: historical (WW2), contemporary (Modern Warfare), futuretrash (Ghosts/Advanced/Infinite), and Black Ops, which is awkward because that name has been used both to sell historical (Cold War) and futuretrash.
What do we have with Battlefield? Historical (WW1 and WW2), contemporary (BF3, BF4), futuretrash (Bad Company, 2042), and crime (the black sheep of the family, Hardline).
Battlefield seems to be sort of doing this anyways, seeing as they only put out two historical before switching back to futuretrash. That's what COD didn't get, they kept putting out futuretrash until the consumer threw a shitfit and refused to take it anymore. But they could have committed to something more like narrative-focused Bad Company games (I've never played them so I have no dog in this fight), contemporary games that don't even bother with their garbage stories, historical games with episodic stories (new war story with new factions), and more Hardline.
I think Hardline's setting was kind of retarded but smaller-scale ones about gangbangers or cartels could have been awesome, the latter has APCs (narcotanks) and some light air support and a variety of maps, the former doesn't really have anything in the way of vehicles but neither do "cops and robbers."