The shooter was already done with his massacre and back outside the church when fired upon. They diffused nothing. The shooter died from a self inflicted wound according to police. Chasing the shooter, guns a blazing may sound like fun but luckily it occurred in a sparsely populated area so no one else was hurt. 

Even if I grant that perhaps the shooter in Texas intended to continue his massacre at another location, the smartest thing that the ones who shot at him and then chased him did was call the police. Any unarmed person could have done the same. 

Speaking of possibly continuing a killing spree elsewhere, the police where hampered in their search to find the identity of the Walmart killer by the ones who drew their guns, this while the shooter was still at large. That information is from the police themselves. 

There is zero evidence that those people protected themselves or ended the killer's rampage prematurely.