Roavin's right. Ideally, a balance would be struck that not only efficiently handles the business of the Court, but also trains several AJs for the role of CJ. This is absolutely possible.

That said, AJ is still a role that requires far less activity than leading executive or legislative positions. It doesn't make sense to firewall the position when it really is a side job, especially when this severely limits the pool of people who can actually perform the job. 

Yes, this creates sinecure. Unfortunately, the other option is to create yet another set of government positions that are firewalled, and just like with the Legislator Committee, such a set of positions will be incredibly hard to fill.