Competitive advantage for an airport? Airports are chosen based on geographical location, not service. Most people live near one major international airport. There isn't some large market of with airports springing up all of the time, they are dictated by regulatory barriers and are natural monopolies.
Passport control doesn't benefit travelers, it hinders them. It benefits the security of the nation, which is precisely the purpose of the general tax fund.
Not at all. I live about halfway between two "major" international airports, each of which is about two hours by train. Or I have a local airport - ten minutes by city bus - with a much more restricted flight selection. If my destination is London, that in fact translates to a choice of five airports at the other end; and if I decide, for example, that Heathrow is my preferred arrival point, that means not only will I have a very different experience depending on the airline and hence which terminal, but also means I can decide between a direct flight from either of those more distant origins, or to take connecting flights, and thus have a further choice to make in each direction when I may be able to choose between changing in Frankfurt, Vienna, Hamburg, Cologne or Brussels. For a frequent flyer there are so many factors to consider in choosing routes, airport competitiveness is very very important indeed. Recently my home airport had me fill in a passenger survey while waiting to board, designed to elicit my reasons for choosing that airport; they hadn't even begun to scratch the surface of the multiple variables I need to take into account when booking flights.
There is a market when you factor in connecting flights. If, say, Delta wants to pay for better staffing at their international hubs they could market that to prospective customers in their non-hub markets.
"Fly home from Europe through DTW where passport lines are under 10 minutes!"
Passport control doesn't benefit travelers, it hinders them. It benefits the security of the nation, which is precisely the purpose of the general tax fund.