It is hardly measurable who truly has faith toward God. It is not the exact doctrine. Christians are saved by faith not the doctrine, but it can be suspicious if they don't recognize the basics. And there are people who have taught correct doctrine but end up not following Christ.To test your assumption, we would need to observe the daily lifes of religious people who believe or not believe in a specific doctrine.
Take, for example, the physical resurrection of Jesus.
How believing vs not believing such doctrine makes people love more or love less God and their neighbors?
Or take the fate of the wicked.
Is the crime rate lower in those who believe in the eternal lake of fire vs those who believe in annihilation or the universalists?
On what basis we say that people who do not believe in X doctrine enjoy less eternal life?
As to less or more eternal life? there is no such thing as having half life. Eternal life is knowing God so if people know Christ they know God. Otherwise they don't have eternal life.