Personally, I've never considered the Audi 5 to be a "true" BMW 4 or Mercedes C competitor. If you think about it the Audi 5 is more GT-oriented than its supposed BMW and Benz "equivalents". It's also heavier, less stable on the track, seats 5 (instead of 4), and doesn't really carry the same kind of racing heritage as the BMW 4 and Mercedes C. It's always been more expensive too, especially in S and RS forms.
Edit: To clarify, the RS5 even without any options has always been as expensive, if not more expensive than, an M4 with Competition package or a C63 with S package.
To the contrary, the Audi 5 is more of an in-betweener. It's positioned above the BMW 4 and Mercedes C, but below the BMW 6/8 and Mercedes E/S two-door versions, depending on the version.
To summarize, the RS5 nearly matches the comfort of a 650i/M850i or an E53 AMG / S560, while nearly matching the sporty enhancements of an M4 or a C63 AMG.
