Here's a basic breakdown of the math of why I think Rapid Brutality is going to be a game changer.

Killer base move speeds: 4.6 m/s or 4.4 m/s
Killer move speed after hit: 0.575/0.55 m/s for 4.6/4.4 m/s for 2.7 seconds
Killer distance after a hit: 1.5525/1.485 meters

Survivor base move speed: 4.0 m/s
Survivor distance after being hit: 15.48 meters
Survivor distance gain on killer: 15.48 - 1.5525/1.485 = 13.9275/13.995
Survivor distance: ~14 meters

Killer base catch up time: 23.3/35 seconds for 4.6/4.4 m/s killers
Killer speed bonus with Rapid Brutality: 4.83/4.62 m/s for 4.6/4.4 m/s killers
Killer catch up with 7.3 seconds of Rapid Brutality after hit cool-down: 16.87/22.58 seconds for 4.6/4.4 m/s killers

Killer time savings per injury: 6.43/12.42 seconds for 4.6/4.4 m/s killers
Killer time savings with 12 injuries (1 per survivor per hook state): 77.16/149.04 seconds or 1.286/2.484 minutes for 4.6/4.4 m/s killers.

So this is why I think this perk is an absolute game changer. Assuming you have a perfect game where you injure, down, and then hook every survivor for a total of 12 hook states, then you'll save ~1.3 or ~2.5 minutes on chases.

Considering it takes 450 seconds or 7.5 minutes to complete all of the generators individually with no perks accounted for, and BHVR have said the average game time is around 10 minutes, that's HUGE time savings! Plus the pressure it puts on the team after getting your first hook. I mean, there's a reason that Lethal Pursuer and Corrupt Intervention are so popular, getting your first hook slows generator progression to a crawl.

And all of that's not even taking into account how this perk might prevent survivors from getting to the next safe loop, or prevent a timely body block, or trigger a Jolt or Pain Resonance explosion before a generator can get completed adding even more pressure and time savings on top of everything listed above.

Unless I've grossly misunderstood exactly how it works, or made some kind of mistake with the numbers, I think at least for 4.4 m/s killers this perk is going to be a necessary perk to run and we're going to be seeing a lot of it.