Actually, Charizard GX is prominently featured in the Meganium/Swampert/Rhyperior/Charizard/Vileplume mill deck that made the rounds after Harrogate, and I even saw someone play it at the League Cup I attended a couple of weeks ago.
But you're right. Charizard has been historically terribly competitively. I think the Charizard from Platinum, Charizard EX with Combustion Blast, and maybe the one coming up in our Team Up set are the only competitively viable Charizards ever printed, and even those didn't/don't appear primed to dominate their respective formats. I think this is because most Charizards are designed to be flashy cards with crazy damage output... but at a really high energy cost. Top that off with the fact that most Charizards have been stage 2s and you can see why it's hard to make a Charizard deck work.
But like I said, this upcoming Charizard in Team Up has some potential. It's hard to justify a stage 2 non-GX in the face of Granbull and White Kyurem filling that niche in the format as a stage 1 and a basic respectively, and in terms of a strong Fire deck in the format we have Blacephalon. But you also can't ignore its damage output, easily dealing 180 each turn and even 210 (enough to KO a Zoroark GX) with a Choice Band. The Jirachi that's also coming out provides some non-GX based consistency that could help keep your deck GX free and allowing you to trade favorably with GX and Tag Team GX decks. And even if it flounders competitively, I can almost guarantee you it will be a powerhouse in the theme deck format.
