"National R&D spending is the main predictor of success in Horizon 2020, a programme which is based almost exclusively on excellence, with grants going to the best researchers regardless of their location"
I have some doubts about the recent statement above just because the data concerning the European Research Council grant does not show that. In the paper in here https://link.springer.com/article/10.1057/s41304-018-0165-8
it is written that since 2007 UK and Netherlands received 50% of all ERC grants in the field of political science. For sure UK and the Netherlans have not spent in R&D the same as all the other countries combined ! Not even joking ! Yes Excellence is crucial still it seems that Not All the Excellent Are Equal ! An Excellent from Oxford or Cambridge has slightly more chances than an Excellent from a less-known university !
See on this issue also the conclusions of the paper below that are not related to R&D spending:
"We do find that the probability to get funded increases significantly for those that have a nearby panelist from the host institution....the effect differs between disciplines and countries"
