Can you show me a chart that doesn't show C series number one or ahead of the aircraft you're using to illustrate your point?
For shorter ranges (hey, you picked 500nm!) then yes because then regionals come into play, with overlapping number of seats:
(Source: Leeham News)
The above graph shows 600nm trip assuming a realistic 70% average load factor. Per Leeham's analysis the E2-190 just edges the CS100 on both per-trip and per-seat fuel costs. The larger E2-195 outperforms the CS100 and equals the CS300.
But really, the incumbents (Embraer, Airbus, Boeing) don't have to
beat the CSeries fuel numbers. They just have to get close enough -- say within 5% -- before other costs like introducing an additional type outweigh the advantages of a more efficient plane.