I actually think the Yor are at least equal if not overpowered. They do require more macro though and are a bit weak in the very early game.

a ) The ability to control growth makes it simple to stay at 100% approval.

b ) Not having to build farms means they have more room for other improvements and can make much better use of lower quality worlds.

c ) You can't build while growing, but you don't have to be idle. Set your planet to 99% science, growth, or military production and get stuff done while you grow.

d ) The fact that growth is tied to manufacturing means that mid to late game their growth can be pretty impressive.

That means you can fill large capacity transports and have your planet back up to max pop in a turn or two.