1st base is the least important defensive position on the diamond when playing 80 games in Wrigley. I get not wanting to trade premium minor leagues for him given his age and position, but let's not make up excuses. Also, he can slide into the DH role pretty easily. He is a great fit for the Cubs, but the price may be too steep.
If they're not willing to let Mervis grow into the position, they are going to have to find a 1st baseman. Playing Bellinger there is a waste of talent.