LOLOL, of course the 707HP car will out-accelerate a 425HP car all else being equal (weight, tires, gears, exhaust)! You are comparing apples-to-oranges and you should know better as a "hardcore gear head".
A more realistic comparison would be the 1971 HEMI Challenger to a 2015 Challenger R/T (375HP). In 71, HP rating were gross, today's net is ~15-20% lower. Therefore the 71 HEMI, which was under-rated at 425HP, but was closer to 475HP is the equivalent of today's 380HP. Google Car and Driver, you will note that the 2015 R/T runs the same quarter mile as the 1971 HEMI Challenger. Which makes absolute sense.
The Hellcat is a factory tuner car. It is supercharged, factory headers, full dual exhaust, has massive high quality rear tires, steep rear gear set and 8 forward gears to optimize operational RPM. The 71 Challenger ran on puny bias-ply tires, 4:11s gears or less, a 4 speed transmission, a restrictive exhaust, a "modest" street cam. If you want to compare apples-to-apples, perform the mods that every weekend quarter mile racer would including slicks, headers, hotter cam, mild head, intake and carb work. These mods would push the car into the 575-650HP range and it would run high 10-11s on high-octane leaded pump gas. If you bored and stroked, fully machined the heads and intake, set-up the chassis for traction, bumped-up compression and run appropriate fuel; sub 10s were the norm .
Just replacing the shitty factory tires with slicks and adding a few traction aids would push the car into the mid/upper-12s.
http://www.roadandtrack.com/motorsports/videos/a7095/mopar-drag-race-better-than-coffee/