- "The mass injected into the Earth escape trajectory would be 4800 kg (without launch adapter), with a hyperbolic escape velocity of 3.15 km/s, which increases to 9.5 km/s after the last Earth swing-by"

The Voyagers were launched directly to hyperbolic excess of >10 km/s — comparable to the speed JUICE will reach on its third flyby, of Earth, in 2029.

https://sci-hub.ru/10.1016/j.actaastro.2019.06.013 ("C₃ of... 105.5 km²/s² and 102.4 km²/s² for Voyagers 1 and 2, respectively [75]")

The mass of JUICE is probably a big parameter here.