If you're not as big and/or good as Embiid and Jokic, or even KAT, or any star FIBA big like Haddadi, you should be good at defense, protecting the rim (which Embiid and Brook are good at, by the way, even Jokic, at least overall on defense), and/or defending PnR. Also, I think Brook, Jokic and Embiid have mobile frontcourt partners with Giannis in Milwaukee, and Gordon in Denver.
Thing is, Erram and Japeth weren't trained to be quick laterally in the perimeter and to close out. Guys like Balti and Tamayo are better trained to switch and better fits as 4s than Erram and Japeth. I dunno about AJ, hopefully he regains his laterals as a 4.
Point is, if we're going to go with a slow guy at center, we need a quick and long player at 4 (ideally 6'6" and up, or at least a Pingris) to cover for him.