So please explain how that is "outperforming" it?
Simply, the detail or resolution from the SX50 at 1200mm is better than the 5DIII +100-400mm at 400mm. If you take a crop from the 5DIII combo to give the same view as the SX50, the SX50 image is better. This is useful if you are taking a bird photo which requires heavy cropping from the 5DIII and 6x less from the SX50.
As I had in the first post, I am not implying the SX50 is better than the 5DIII but the extra reach at 1200mm beats out the 100-400mm at 400mm. That is quite remarkable and unexpected to me, and it means I can travel light. Normally, I would use the Canon 5DIII with a 600mm prime, and only use the 100-400mm when I had to travel with limited luggage. But, for work trips I'll just take the SX50 for from now on knowing I can get some spectacular shots.
5DS R, 7D II, EOS-M, Powershot G3 X, 300/2.8 II, 1.4xTC III, 2xTC III, EF 35 f/2 IS, EF 70-200/4 IS, EF 24-105, 15-85, 100-400 II, Sigma 10-20, EOS-M 18-55, f/2 22, 11-22