The regular season absolutely matters. It might not matter to you, but you don't speak for the basketball universe.
Most people complained, and still hold it against him to this day, that Cuonzo barely snuck into the NCAAT with JRich, Stokes, and McRae, despite making the S16. And that is justifiable, IMO. No one excused the disaster of a regular season because of the postseason success and none of the anti-Barnes crowd are going to excuse him from some of the inexplicable losses this year if this team makes the S16, or better. It will be, "How did this same team get embarrassed by an awful UK team at home!?!?", just like eight years ago when it was, "How did Zo and co. barely sneak into the NCAAT with those players and level of experience?".