The most dangerous words in a client relationship are not 'we made a mistake' — they are 'that was outside our scope.' Partners who reach for scope as a shield when results disappoint are telling you everything you need to know about how they will behave when things get hard.
The agency model is broken in a very specific way. Not universally, not irreparably — but in a way that most clients feel and few suppliers acknowledge. The break is in accountability. Specifically, the systematic avoidance of it.