What are the chances of the WD Hitch wearing out my trailer's coupler latch?

No problem there. Couplers are designed with a high safety factor. The jarring forces of braking and taking off are far greater on your coupler than the steady force we are applying.  Also, depending on the coupler design, we actually drive the ball up high into the socket, so for 99.9% of couplers out there the force is on the rear upper corner of the coupler instead of the latch assembly.