IMHO, a lot of people do not necessarily train with self-defense in mind. Aikido is flexible enough to be good exercise and an opportunity of self-transformation. It may take longer to become good at self-defense in Aikido, but it sure is possible. many of us at The Tenshinkai Aikikai Dojo in Westminster, CA have belts in other forms of martial arts. We train pretty hard and get a sense that yes we could use it. Several already have. I guess it all depends on why and how you train. And yes, there are actually several more reality based systems that have a great background and foundation in Aikido.
Nidan Tenshinkai Aikido
Lucaylucay Kali JKD