Ares TTK (0-30m)

5 shots to kill (shot 1 comes at t = 0s) = 4shots/(13 shots/s) = .307s

Vandal TTK (see edit below)

4 shots to kill (shot 1 comes at t = 0s) = 3 shots/(9.75 shots/s) = .307s

Phantom TTK (15-30m)

5 shots to kill (shot 1 comes at t = 0s) = 5 shots/(11 shots/s) = .364s

(Yeah these engagement ranges are cherry picked but they're common and frankly it shouldn't have a faster ttk at any range.)

What was Riot smoking when they thought this was a good idea?

Yes, the Vandal/Phantom can 1-2 shot to the head, but the problem is the low effort required to beat those weapons with the Ares with bodyshots. The recoil pattern on the Ares is minimal, and the spread (random inaccuracy) is high, inherently making it a low skill weapon that encourages spraying to the body.

A $1550 weapon should not be allowed to do that.

Edit: It's been pointed out that the Vandal's firerate is actually 9.75 rounds/s, not 9.5 rounds/s, giving both weapons the same ttk to the body from 0-30m. Calculations above have been edited to reflect this.