AR's murder needed to be shown not just mentioned. His character was there since season #1 and his murder should have been depicted much like Maranzano or Masseria's murder. Frank Costello became a poltical fixer/powerhouse after AR was killed, and was a Partner to Luciano and never was mentioned in 5 years ?

wise old owl sat on a oak , the more he heard the less he spoke , the less he spoke the more he heard , wasn't that a wise ole bird.