Well measurements of realism are subjective in many ways. To my own standards, Proportions is much more realistic.
For the specific example of population growth, I think of population as a semi-abstract mechanic, and in practice, planets in Proportions are almost never "full" - when they are, it abstractly represents the limit of an environment to support more (abstract) useful civilian elements.
Not that this is on-topic. Maybe an admin could move these Posts to another thread, since they've sidetracked this one.
PvK