Gravity is essentially how much attention the defense pays you when you don't have the ball. It's usually shooting, but can be from a roll man on a pick and roll, a cutter, etc.I honestly had never heard of it until that tweet.
Hawkins had the most gravity I've seen in college since Steph Curry. Steph Curry one game in college got double teamed all game even when he didn't have the ball.
So that tweet was saying that since most of the players on Kansas aren't catch and shoot threats, the defense can collapse and not have to stick on their men. Of course, it's misleading. The tweet specified catch and shoot attempts as a proportion of total shots taken. When you assemble a super team, your guys are coming from places where they had the ball a lot. So for example Zeke Mayo didn't have a high ratio of catch and shoot. But he did shoot 39% on 3s, it's just that half of them were off the dribble. Kugel took more than half his 3s off the dribble. AJ Storr only shot 32% from 3 this past year (but 40% the year before), but he still took 150 3s (but 50 of them were off the dribble). He's still good enough to be guarded. It's harder to shoot off the dribble. Transitioning to more catch and shoot 3s is easier. They will likely all shoot a better % this year. Dickinson also has to be guarded from 3. Harris will have to be respected at least a little. Their shooting is fine, and they're probably bringing in Griffen or Brea as well.