You'd never hear a basketball player ask "how well do you think basketball-do prepares you to play a game of basketball?"
A thought provoking analogy but it doesn't really apply to the field of self defence. A game of basketball is not an unexpected life-threatening event. That is the core problem with discussing the effectiveness of any martial art - it is rare (thankfully) that we have to put it to the test. Sparring and grappling - all that "live" training stuff - might
be useful but who was it said "In theory there is no difference between theory and practice. But, in practice, there is."
I don't train for self defence so it's not an issue for me. But if you were serious about SD, you need a bigger toolbox than Aikido provides. A serious fighter should be very fit and have some experience in a more physical throwing art (Judo or Jiujitsu) and a striking art (boxing or Karate). Aikido can add a lot to that but I don't believe that those who know only Aikido really have much hope in SD.