This is more about accountability and commitment. Advertising is a contingent business. Agencies are retained to work for their clients who rely on them to deliver awareness and sales. Clients sign off campaigns, so work that others see as bad has been agreed by the client. It all comes down to the talent you employ and the leadership of the agency. As for Trivago, you could say that if their message is 'ideal hotel' for the 'best price' - they get their message across.
That it takes just as many people to make a great ad as it does to make a shit ad. Obviously the quality of those people is imperative