Well, I believe none of us seriously learned Aikido purely for "self-defense". In our days the best thing for self-defense is a smart mind first and a gun second. Considering that, then Aikido really is one of the best art to learn for self-defense, because it teaches you environmental and situational awareness.
Is any Aikidoka crazy enough to go hand-in-hand with a trained boxer? I hope not unless again, you have a gun. But Aikido does train you to recognize the danger of the situation to back away before it's too late or possibly escape. That's something I value. I won't be standing there arguing with a guy who look like he's gonna freak out any time.
My Sensei used to tell us, if you are really really good at Aikido then you will never truly have to use it, because you will simply not be there when the fight happens. Unless you are Japanese riot police, but that's another story