Actually, marketing firms come up with their own campaigns, without any help from "lobbyists", and usually without any help from the corporations. That is what they do, they often are good at it, and they get paid for marketing campaigns, by companies. The marketing folks that work for marketing companies are MBAs, the run the business, they are not marketing experts, which is why they pay marketing companies to contrive the next campaign to push sales.
And yes, these MBAs approve the marketing campaigns, they usually are presented with 3 or 4 ideas on "story boards" and they go, usually, with one. The idea is created by the "creators" (literally) at the marketing companies. I've never ever seen a lobbyist at one of these meetings.
I did work on the fringe of a lobbying effort, we were trying to explain a patent issue to our Congressman in DC. It was entertaining. I was involved in a few meetings with our lobbyist and had lunch with them where everyone was interested in what kinds of things he did for the company. He never said anything about eating this or that for breakfast of course, and we actually had a foods business at the time.
I thought most of our ads were incredibly stupid until I had the concept behind them explained to me. I still thought they were sort of stupid but I realized they were not intended for folks like me. I'm old as dirt and a bit odd.