Ha, the thumbnail for the second video is convincing of GG's form. You are right the off-arm looks off.
You look like you're pushing down with your left arm, like you are trying to get out of a pool or climbing on a box. GG looks like he pushing off a ski pole, which reminds me of the lead arm when uphill skating skiing. I realize this might mean nothing, even with the images below, if you've never skied... Though I feel the imagery illustrates the point that you are (possibly) "sending momentum" up by pushing down while GG is "sending momentum" forward while pushing back.
https://imgur.com/a/eDssL93
https://imgur.com/lL7Vr6U
That's interesting, thanks! That actually speaks to what's been one of my big internal struggles with this, what essentially that left arm move even is. It's a swim move, but also a drop, but also internal shoulder rotation, but which of those is driving the power? Or is it all three? There's a really hard-throwing kid somewhat local to me, Bradley Oberholtzer, who's interesting to compare to GG because of the similarities and differences. It's interesting to see him externally rotate then internally rotate both shoulders at the same time, in the backswing and then the swing. Maybe I'm answering my own question, because his left arm doesn't do anything similar to what I was trying to do the other day. Anywho, I'll try skiing!