this is a very intersting read and highlites the debate between form and weight. Im in the form camp and believe get perfect form and slowly build up. My gym owner who competes and fucking massive always says bench upright and let the dumbells gently touch your shoulders as its those 2extra inches that make the muscle work and grow.
We train to compete. Not me personally as i dont have the time or money which is why the bench HAS to be upright so it isolates your shoulder. No point in tilting in back slightly as that brings your upper chest in to play. Fine if u just wanna get strong but not fine if u need to isolate particular muscle groups