Although his son was better, XYS was (marginally?) weaker than MRB

1. MRB executed perfect defensive stance to defend himself from SM. XYS couldn't do better and gave up.
2. XYS was willing to listen to MRB's proposal (if he was stronger than MRB and his son was stronger than MRB's son, then why negotiate a sure-win?)
3. MRB was already famous for his skills since a tender age.