Dumbed down from what? There's no prior game in the series.I can't put into words how much I hate fixed growth. Dumbing down things to make it simple is one thing; dumbing down that things that negatively affect gameplay is another thing entirely and is in no way fun.
They were designing a new game and picked a simple population growth mechanic to control the rate of improvements. It avoids having to micromanage cities, which would get horribly tedious late game. Being able to focus on the military part of the game is nice.
I see room for improvements, but I'd rather have the game stay like that than become a micromanagement nightmare.