You make some good points. How about improving the conditions for fire? The friction may not be enough to ignite, but it could be enough to increase the dryness

You make some good points. How about improving the conditions for fire? The friction may not be enough to ignite, but it could be enough to increase the dryness both through friction and mechanically brushing away water. By stripping small bits of bark surrounding the area around the contact point it could create an area that would be more predisposed. Although upon reflection I think the fire hypothesis is remote. Although, I could see it causing enough damage over time to restrict the victim tree's growth on that branch, or even killing the branch outright due to damage or disease caused by the injury. If the aggressive tree had adaptations that reduced its susceptibility to disease it could be a net win.