"realistic" is an interesting word, because it can have different connotations.

We can write a very accurate quantum mechanical model for the oxygen atom. But you can't actually simulate it without a galaxy sized classical computer. But it is very realistic=accurate model.

Or you can write and easily simulate a non-realistic semiclassical model. This one is a realistic=efficiently simulatable model.

Obviously a fully agent made model is more realistic in the "accurate" sense, because it correctly models the underlying reality. But if you make realistic agents, you have something inefficient (non realistic in the "simulatable" sense).