I suspect the best thing is to focus on the biz, it's much more important to have a big pie to argue about dividing than to have a fair division of nothing
Agree with this, whats done is done. Keep pushing forward and keep an open mind about his opinions, you never know when a piece of advice from an 'outside' mind might help. Just because he may not have been there during the formative part of the biz doesn't mean his thoughts about it can't make everyone money and see things that other people wrapped up in growth don't see. Hell he/she might even turn out to be an asset as they don't see the day to day and also know you and your other partners faults via the slow time.
Agree that the best thing is to focus on the business and maximize the pie.