Who's talking about variable gear ratios?
GM is. They’re saying that there is no coupling of the engine to the drivetrain through “a fixed gear ratio.” There is a coupling of the engine to the drivetrain through the planetary, and the opposite of a fixed gear ratio is a variable gear ratio.
After the Clinton administration, I became very adept at parsing PR written by lawyers. And that’s what this is: PR written by lawyers.
If the vehicle were “all electric drive” the engine would have no way of transmitting power to the drivetrain through any geartrain.
The engine would have an alternator (or generator) fixed-coupled to the crankshaft and the alternator would charge the batteries, which would then drive the electric motors which are coupled to the drivetrain. That would be an “all electric drive” vehicle, just as diesel-electric locomotives have no mechanical coupling of the diesels to the wheels. That’s an example of all-electric drive.