Are all nips the exact same? (one shot)

I recently bought two nips to try (Malibu and Jack Daniel’s honey whiskey) but on the bottle their measurements are 21% alc/volume and 35%alc/volume respectively.

Doesn’t that mean the Jack Daniel’s basically has more alcohol? Are they not both supposed to be one shot? Or is it supposed to be “close enough”

Is it like that for every brand?