In the world of Big Data, Engagement metrics, ROI dashboards, Brand Equity measures and Financial performance (pick your timespan, from day-part to decade), your observation of what's 'messy' is spot on. To paraphrase your piece, it's essentially about complexity about the known and mystery about the source and impact of change. "Anticipating the unexpected" is a non-sequitur of course, but Strategy is the bedrock of how to deliver contingenices within the corridors of brand purpose, fiscal focus and competitive advantage.
 
CEO's are not wrong to ask for perfection: "Man's reach must exceed his grasp, else what's a heaven for?" That said, they also need to enter into a contract with their Marketing leadership about how to navigate to ________________ (whether Revenue, EBITDA, Share, Klout scores, et al). Past that, you're right -- it is largely about Tactics, but also about allocation, persuasive content and aligning demand fulfillment systems / channels to exploit increased purchase intent. Those elements will differentiate performance and distinguish great marketers from mediocre ones.
 
The good news is there are empirical methodologies that sort through the 'mess' to trace the right drivers of brand health, pinpoint how to enhance them, then optimize resource allocation for maximum short-term financial growth and long-term brand strength competitively. (Full disclosure: Keen Strategy does this.)
 
In years past, the path to success was linear: Share of Voice, Award-winning creative, Distribution scale and purchasing power / margin management. Differentiation and innovation take more forms now, from many different sources in the value chain (including the consumer). 

Messy, yes. Manageable, sure -- with the right strategic vision and tactical flexibility. Here to stay? Absolutely.