Runners are at a huge advantage when they have competed in two or three 'big city' marathons.
You get certain competitors favouring certain cities and sticking to that race. They get comfortable and it helps massively knowing when to make the right moves during the run. Olympic marathons are a real leveller because it is rare for people to have previously run the course. But there are a lot of top athletes running this year. Portugal's Antonio Pinto likes competing in London.