Bérubé pointed the finger at agencies, which he accused of not doing enough to maximise the return from their main asset – their people.
"When you think about an agency, you don’t sell a product – what you sell is the quality of your people," he said.
"I’m always surprised when I see agencies that don’t even have an HR department with a training manager that is responsible for training the people. Most people join agencies as experts, but they leave and they’re not better than when they joined."
Bérubé, who replaced Hugh Pile in the role in August, was giving the keynote address at the ad:tech London conference today.
He argued that as digital tech became more established, the industry had moved from a phase in which general digital capabilities were at a premium to one where people need to be able to exhibit more finely-tuned knowledge and skills.
"We needed digital experts from maybe 2005 to 2015, because no one knew what digital was, we needed a bit of upskilling," he said.
"Now what we need is not a 'jack of all trades' – an 'agency of all trades' in digital – we need expertise, which is very different. I don’t want a digital expert – I want a precision marketing specialist. I want an audience manager. I want a community manager."
Bérubé said L’Oréal was staying ahead by ensuring that its staff across all disciplines – such as marketing, sales and finance – were trained to "be able to understand the world we live in".
He added: "We have to get better by bringing in experts – but if you want to retain the experts you hire, you need to train them, develop them, and that’s a very difficult thing to do. That’s something we take very seriously – to train our experts to be best-in-class experts."