The achilles heel of Scrum is that it sold out the prescriptive XP practices that enforce sustainable software engineering discipline as well as communication with business concerns in order to sugar coat the fast feedback cycles. Scrum/Kanban feedback is about "doing the right thing". XP feedback is about "doing the thing right". Codebases on projects using Scrum/Kanban without XP technical practices tend to molder and succumb to what I like to call "Scrumrot" within about 18 months. Seen it happen many times.