Ref https://wildfiregames.com/forum/index.php?/topic/25184-task-current-issues-with-celtic-units-and-guideline-for-the-next/page/7/&tab=comments#comment-393215

also reason cost is 2 rotarymills and reducing effect even under one rotarymill is wrong

You're right the new technology is a more expensive than the first two gather grain technologies. However, the idea is not to be more cost-effective than the default technologies; it's an extra technology that can give Gauls an advantage; the exact cost is not that important.

Move to village phase and increase the gain to 20%. Will be a more useful tech and more consistent to "high" cost.

wouldnt moving 20% bonus to phase I make gauls more op ?

Hmm, maybe...
What about 200w100m 10%, village phase?

I would not move it more earlier, mill was phase III structure and even now this tech is phase II.

In rP23803#46385, @Angen wrote:

I would not move it more earlier, mill was phase III structure and even now this tech is phase II.

Ok, and about values proposed by me?

I could agree with them

Looks like Belgian Bog still has them

In rP23803#53543, @Angen wrote:

Looks like Belgian Bog still has them

Yes and that's intended as eyecandy.