I guess to settle this question, yes the answer is they are both very Amercanized versions of the show Science Ninja Team Gatchaman.

There was also Eagle Riders, which took stuff from Gatchaman 2, and G Fighter (the show was briefly on in the early 2000s).

Though to not confuse anybody, G Force is also called G Force Guardians of Space (probably so it won't get confused with that hamster movie called G-Force).

IIRC on Battle of the Planets the team was also called G-Force.

Anyhow BWBoddy is up!
Toho's Godzilla Will Live Forever!