Reducing seating capacity at arenas/stadiums is a current trend over the last decade of in the industry. We're seeing it across the board. New downtown arena is another example where it will have less seats than the current Paycom. I completely understand professional vs college, however the function of the space is the same. The buildings that have put in less seats, with more of a luxury and greater amenities flavor, are currently more profitable.
Having these massive buildings that sit empty for a long portion of their life doesn't benefit anyone. Just remember, OU will only occupy this for a minority of the year.
Trying to be optimistic about the project, I think it's important to make sure that they can try and fill it with events other than OU sports, as that is what will need to happen for a large chunk of the year. IMHO, Norman and the soutside of the metro can not support a 10K arena. The closer it creeps to the downtown arena size, it makes less sense. There is potentially a narrow market for the 8K type size arena, that would make sense for other entertainment (concerts, events, conventions, etc) to use. Much larger and you're competing against a bigger group of arenas in the area.
There is a reason why the state fair arena is the 6-8k range, and Winstar seats the 6k range. It's more realistic to fill with concerts, etc, at that size.