I think the only real way to find an answer to this question is to give it a try (for quite a while) with an open mind.
no matter how many times I or other people tell someone that it is effective it means nothing. the only way to understand it is to experience it and descide if your aikido can be effective in the situations you describe.
the question isnt really, "is aikido effective?" it has been shown to be effective by many different people and groups on many different occasions and in all of the situations you describe. the question is... "can my aikido be effective in those situations?"
Train and find out