Surely the fundamental mechanical purpose of any martial art is self-defence/combat.
Of course Aikido evolves from this basic concept but that's where it starts
(Apologies for the thread drift)
Style doesn't matter - instructor and students attitude does
O sensei changed basic mechanics of daito ryu techniques by creating multiple openings to allow developing his spiritual concepts. That's one reason.
Another one, self defense/combat implies real skills in street fighting. No aikido style teach fighting any nature, not even sparring (which should be first step to get real skills in fighting against countering opponent, second would be go to the street and get real fight to test your skills…)