Adam,
Associates (and shapers, too) can have a lot of influence if the boss lets them. Some architects may treat them more like babysitters, but I figure if I'm paying them they had better be contributing something more than that.
An architect who doesn't let the associates out to play is basically saying that he can design the entire course himself in however many days he is on site.
As to what each associate contributes, I think you would get three different answers on any job if you asked the associate, his boss, and the client. Trying to speculate about what happened 75 years ago is pretty tough, when you can't even figure out what's happening today with everyone involved still alive.
Some people insist that Perry Maxwell would have been nothing without the Wood brothers; a member of the crew at Crystal Downs would have insisted that MacKenzie was nothing without Perry Maxwell.
P.S. I just got back from pizza with six of my associates, two interns and one ex-intern, all nine of whom will be on the equipment in Washington for the next two days. The point of that arrangement is so they can all contribute something to the job while I'm here to look at it and provide some input on what they are doing.