Using Ryu represents a purist (and arguably sadomasochist) approach to Street Fighter 4. Whilst he was acceptable in Vanilla, his competitiveness as a character peaked in Super then rapidly diminished with the release of Arcade Edition (AE). This is not to say he is not a viable character option; rather, he represents a style of play that is heavily reliant on a competent understanding of core gameplay fundamentals in order to evade some of the more tricky situations players might find themselves in (Dan is somewhat of a more extreme example of this).
Fists of Fundamentals
Capcom seem determined to paint Ryu in AE as a "bridge" character for new players to use solely as a platform to become confident in the use of core gameplay mechanics and execution. By giving the player only a basic set of tools that don't excel in any particular area, the player is forced to fall back on their understanding of gameplay mechanics in order to remain competitive against much of the cast. This is of course, Ryu's biggest failing and the main reason he is not viewed as much of a viable option for competitive play. His lack of shenanigans and offensive capabilities in what is arguably a very offensive game put him at a severe disadvantage in the eyes of many players. In addition, the fact that a certain Japanese player also left him in favour of Yun while publicly stating "It's over for projectile characters [in AE]" to Famitsu magazine certainly didn't help things. This turn of events was not necessarily bad, however it did provide the impetus for many long-time Ryu players to finally consider a switch. The case can still be made however, that pursuing Ryu in a consistent fashion provides immeasurable benefits to a player's fundamentals, more so than any other member of the cast.