morality has to be (or tend to become) not only (more) consistent, but also (more) complex

It's not clear to me that one can usefully distinguish between "more consistent" and "less complex".

Suppose that someone felt that morality dictated one set of behaviors for people of one race, and another set of behaviors for people of another race. Eliminating that distinction to have just one set of morals that applied to everyone might be considered by some to increase consistency, while reducing complexity.

That said, it all depends on what formal definition one adopts for consistency in morality: this doesn't seem to me a well-defined concept, even though people talk about it as if it was. (Clearly it can't be the same as consistency in logic. An inconsistent logical system lets you derive any conclusion, but even if a human is inconsistent WRT some aspect of their morality, it doesn't mean they wouldn't be consistent in others. Inconsistency in morality doesn't make the whole system blow up the way logical inconsistency does.)