There has never been an instance (that I can find) that would indicate that the Defiant could pull off generating a gravity well on par with a warship with massive systems dedicated to the task.
The one film became the main trait of the Falcon's hyperdrive (that it's super fast, but also relatively unreliable) in the EU, but it's also important to note that not only was it down for repairs at the time, but the Rebels had been on the run for quite some time at that point, and proper maintenance is hard to do when you have to pack up and run every couple of weeks.