He didn't win every race. Last year there were 5 different race winners. Schumacher, Rubens, Kimi, Trulli and JPM. 5 different drivers and 4 different teams won races. That's pretty darn good in F1. Yet for some reason that wasn't good enough for the FIA and they felt the need to damage the sport even more by rolling out these utterly ridiculous new endurance race rules.
And Schumacher is the best, of his generation. Senna was the best of his generation. I don't like to compare them head to head becasue they were of different generations, different cars, different rules etc.