I greatly disagree with that. Imo the Kobe Face was created out of pure chance. Imo, it first came up late in Game 3 of the WCF between LA and Denver, right after Kobe hit a clutch 3 over J.R Smith to give LA a one point lead.
This is the moment I'm referring to.To me the face came out of;
A) Kobe being exhausted, as he was drawing long breaths. I've always found, at least with myself, that when I'm running on fumes and drawing deep breaths that my jaw tends tends to protrude and that I bare my teeth.
B) The guy wanted to show agression. He'd just stuck a dagger into the Denver team and wanted them to know it. So as I explained earlier, since his jaw was already protruded and his teeth were already showing, he decided to extend it by clencing his jaw to give himself an intense look.
Now what I think happened was that after that first inadvertent time it happened, people started telling Kobe that it was such a great look, to the point where, as you said, he probably spent time in front of the mirror trying to perfect it. But whatever, MJ probably spent time in front of the mirror working on his pist pump. It's what the great one's do.