Due to how matchups in the first round of GCS are determined this dataset can, at best, tell you what factions the best players prefer to play as.
e.g., if DevM's favourite faction was not USF, the winrate for USF would go down, etc.
You can expect to see more-balanced matchups starting from the 2nd round and above.
Tobis vs Andres and Theodosios vs Refero seem to have been more evenly matched than the other matches on that round. (I've only watched Tobis' matches though).
Definitely. Just, given how much bullshitting that's been going around lately, one could imagine not even VonIvan playing Soviets would be able to beat a monkey playing Axis