I'd say illegal screens directly effect the ability to play defense much more than carrying or traveling do.
I'm telling you man, if you do anything enough times in the NBA the refs won't call it. Definitely, people underrate how much it affects things. Especially for a team that is moving off ball constantly. It is the result of many of their open shots. I don't care what anyone says, if Miller or Ray Allen could play on this team they'd be dropping big numbers too. Now, that's not to say Curry isn't special. There has never been a player that needs so little space and time to get off his shot than him. So we know he's ungaurdable one on one. Many players are...but not many players are so unstoppable that a team defense can't slow them down. Like a team can stop Harden. funnel him to your shot blocker and force him to take outside shots. You can't stop Curry as a team because if the man guarding him tight is screened his teammate has to rotate over to Curry...by then it's too late.
If they called carrying like they did back in the '60s, guys like Allen Iverson and Steve Francis might never have made it to the NBA. Even if they did, they would never have been stars like they were.