The free builder is right on city settle and enables turn 1 chops sometimes. You just settled territory, it’s unimproved and they give you the solution. Plus 50% settler build rate in the GP city which can be great efficiency paired with magnus and or that +50% card. The reward is instant and concentrated where you need it. the Warlord throne bonus can be larger in production terms but it’s delayed until you actually capture something, and it comes later in the game. Plus it’s equal to one turn of production in each city across your empire. (20% for 5 turns is 100% for one turn.) One turn! The reward is spread out over time (5 turns, in the future) and is dispersed across your empire. If it was like, get 20% of your empire production as a instant chop in the city with the throne, even though the overall effect would be just 1/5 of now, I think it would be a lot more impactful due to concentration.