You can not explain the much higher GDP/oil barrel of Japan versus US because Japan manufactures less than US. Nor can you explain the declining oil intensity of OECD countries because they are importing manufactured goods from China. Even if all of China's oil consumption was included in G7 countries, they would still would have decreased oil intensity in last 30 years.
A lot of manufacturing doesn't use much oil, think of steel( coal), cement(coal) plastics( natural gas) aluminium( electricity). What uses oil? ; transportation especially cars and trucks, air transportation. Rail and ocean transport only uses a very small portion, and in most countries almost no oil is used for electricity production. Some oil is still used for heating homes and offices, but this use is being replaced by electricity or NG.
If oil prices continue to increase, its reasonable to assume continued improvements in GDP/oil barrel, in fact improvements in GDP/energy unit, although there is no reason to think that energy use will decline as oil use declines.
China doesn't have to reach the 12 barrels/capita, because they are building high density cities with mass-transit infrastructure.