The problem is that Charizard can't switch between them freely. Stealth Rocks aren't hard to get up in NU, with Pinsir and Gligar now running around with even more freedom. Charizard needs support of a Rapid Spinner, and while Spinners can help the team on the whole, having to dedicate two slots for one sweeper is done better with double screens and belly drummers.
What about Muk? I've used it a few times, and now that Espeon is gone (I've taken it off my team, and I've seen a few others do the same), it can get a Curse or two under its belt before dealing with anything. With pure Poison typing, it doesn't fear any Toxic (so long, Articuno), and with priority as Shadow Sneak, it can smash any frail revengekills. Too bad it doesn't have reliable recovery, though.