You only mentioned china, where they don’t report on land costs because all land is state owned but yes I do believe land compensation is much less in china, not least because HS2 land compensation is significantly above market rate. Also; an authoritarian regime with only superficial regard for the health and well-being of their workers, that are paid almost nothing is certain to be cheaper. Suggesting otherwise is banal.
When my beloved Arsenal built the Emirates, people said that they were low-balled. That claim is part and parcel with any forced possession. However asking you to prove that the valuations were low isn't asking a lot.