I would imagine part of the sell to get Z to come back would have to be that he will get more minutes in general, so yeah that'd mean more minutes with both twins on the floor.
The weird thing with Z on defense is he seems to move very well for his size, and thus is more capable than Tomi at guarding in space, and can make up for getting beat by being super long with good timing and explosion to contest a shot... But he's such a good shot blocker that you'd rather Z be the one protecting the rim instead of Tomi and not be guarding a 4 in space. Kind of a weird dynamic.