I agree about Joselu in that he's not good enough but Mitro has also had chances. Maybe the West Ham post match ban incident, albeit handbags, was the final straw for Rafa in that he'd only use him now in emergencies.
I would stick him in , I think the Bournemouth centre halves are old school and Mitro would relish an old fashioned tussle. As stated above a loose cannon but surely would offer more threat. Added to the previous partnership with perez both seemed to like playing along side each other.
Joselu is shit and Perez seems to play no more than one good game in three, so as we all knew in the summer, we're toothless upfront. Problem with Mitrovic is he just doesn't learn and can reduce us to 10 min within 5 minutes of the game starting the thick fuck, that said there's no reason for keeping him off the bench, can definitely make a difference on 60mins.