I think you are wrong to dismiss that point so harshly, when all empirical data shows it to be true. Engineering, Hosting, Marketing, Monetisation, all those things are massively cheaper when done by one big player. There is a reason publishers outsource advertisement to those shitty networks: They would be overwhelmed by the cost to operate, let alone create those beasts. And even when this problem would magically go away, they still lack the access to the petabytes of data the big platforms enjoy. Without this data, the advertisement will necessarily be crude and lacking focus.