Found this, not sure if legit.
So, after having done some research on Hardline, it apparently gives a 20% bonus to your kills and 25% bonus to objectives, from what I've seen at least. Meaning each kill gives you 120 points in TDM instead of 100 (60 points in others) and 250 points for capturing a flag instead of 200. So, from the looks of it Hardline gets better with the higher Scorestreaks. It's not as useless as I first thought, it just seems that way because everything costs about a kill's worth more this game than previous games, meaning Hardline just brings things back to the level of previous games. I decided to list the amount of kills needed before and after here for easier reference. Hardline doubles in effectiveness once you hit 1200 points (VSAT) and then triples for 1900 points (Swarm). Obviously, this is for TDM and will change in other objective modes.