I don't see the problem? It's probably much more expensive per impression than traditional advertising, but probably much less expensive per sale (which is the metric that matters). This arms race means that if I'm a plumbing supply company, I can now spend my money on displaying ads for specific plumbing goods to people searching for specific plumbing goods, even when that means I'm going to hit some people no longer in the market for these goods -- but even hitting people who are no longer in the market is vastly better then hitting people who were never in the market. This lowers the barrier to entry (less cash required to advertise your products) which means more and better competition which means prices go down.
They don't appear to be targeting people who are in the market for plumbing supplies and hitting a few who already have them, from what we can tell. They appear to not be targeting people who are in the market at all until after they're out of the market.
The only places in which people are really competing directly with each other are in the labor market (which drives the price of labor down) and in professional sports or other one-on-one contests.
Almost everywhere else we co-operate before we compete.
So far this model is a bit like democracy, it may not be optimal but it seems to be the best we have. If you can improve on that model you'll go places but you're going to be ironically in competition with everybody else!
Also interesting note: from my experience, most tech companies aren't really competitive. The market is big enough that most successful companies either compete superficially or sometimes outright cooperate, even when working in the same market.
It doesn't matter if it's proven or not. We're (hopefully) not automata just doing what's proven to make us excel without consideration for the others.
And that's in a nutshell both the solution and the problem because users have only so much to spend on product. So you end up with an arms race and that's exactly what we are seeing.
It's like the joke about two guys in a jungle, one with boots, the other with running shoes. The one with boots asks why are you wearing running shoes. The second one answers: In case we get chased by wild animals. "You won't be able to outrun a wild animal so don't bother, wear boots". To which the guy with the running shoes says: "I only have to outrun you".