In The Wealth of Nations, Adam Smith first describes the economic value of specialisation: "The division of labour, so far as it can be introduced, occasions, in every art, a proportional increase of the productive powers of labour."

This simple idea – that dividing work into precise jobs for people means the same number of people can do more – has been one that has driven the manufacturing age. It's visible in everything from the manufacture of pins to the modern-day assembly lines of Henry Ford and has been taken to its logical conclusion in the Japanese philosophy of kaizen.

It has also become increasingly visible within the world of business; in marketing services and even clients' own marketing functions. Specialists have been cropping up everywhere. Holding companies have diversified their offerings, and their agencies have built departments within departments. Disciplines have birthed specialised versions of themselves. (The planner begat the comms planner. That begat the digital planner. That begat the social planner. And so on.)

All this specialisation would suggest the industry is becoming more productive (and therefore profitable) and that it is making marketing both more efficient and effective for businesses. Yet all the evidence suggests otherwise.

Holding companies may be driving more revenue from selling more services, but there is little sign of increased productivity and profitability, and there is an increasing body of evidence that marketing (on average) is serving brands and businesses more weakly than before. All this specialisation has simply fragmented brands into a million little pieces.

Perhaps marketing and the entities that serve it have been following the wrong development plan, since it has been built on the wrong economic diagnosis. We should not forget that marketing was born in a post-war manufacturing world, but increasingly, we are operating in a post-manufacturing world. As John Willshire eloquently points out, if that is the case then perhaps marketing does not fulfil the criteria that makes the division of labour beneficial.

There's an urgent need, in my opinion, for the return of the informed generalist – marketers, and companies, that serve them, who are able to see the whole picture and design the right solution, unencumbered by the chains of specialisation. Who are obsessed by the outcomes they create, not the output they make. Who can join up thinking and deliver a solution across time and space. Who are able to zoom in and out in order to see the forest and the trees.

Marketing needs to return to a place where it is about the 4Ps, not the single P of promotion. It's shocking to see how few marketers today are genuinely able to control and influence the product, its pricing and placement.

Specialisation is driving a wedge between the commercial imperative and the creative solution. Laurence Green, a partner of the agency 101, summed this up brilliantly:

"The task of any imaginative agency, any creative company, is to understand and serve its client's business problem. Too often, our business has sliced and diced its tasks in the style of a sub-prime mortgage bundler.

"A corporate task set by the chief executive, reframed as a comms task by the marketing director, refined by the brand consultancy and reduced by the ad agency to the stuff advertising can do: grow awareness, nurture engagement.

"Too many links, too indirect and weak a connection between commercial possibilities and creative resolution."

You could argue this type of adviser already exists, in the consultants to which CEOs are increasingly turning. If so, it's sadly a symptom of marketing's retreat downstream. Marketers, and their partners, need to swim upstream. Perhaps the bigger and more provocative question right now is whether marketers and their advisers are able to pivot out of the fragmented mess they find themselves in today.

Companies ask marketing to create demand that drives a sustainable business. They want marketing to grow their business and solve big, tough, complicated commercial problems. We would be wise to remember Ted Levitt's maxim that 'people don't want a quarter-inch drill. They want a quarter-inch hole'.

It's time to stop the fragmentation of marketing and get back to our true specialisation: growing businesses by getting more people to choose you, and use you more often. By whatever means necessary.