Flying, gravity-pulled Titan decks usually seem pretty good on paper, but in real games they're not as invincible as they look. There are actually a bunch of ways to deal with a high hp creature (e.g. mutate, rewind, freeze, shockwave, antimatter, etc.). In addition, a flying Titan deck won't be terribly fast so that it's actually possible for the opponent to set up enough continous damage to kill your gravity-pulled Titan relatively quickly (esp. false gods). This causes your killing speed to drop, and eventually you're over-run.