There is an extreme position that all people in all societies have an equal chance of salvation, that the quantity of devoutness is fixed, that there are always about the same number of Saints at whatever time or place in the world.
Such a view is wrong: it denies free will of individuals on the one hand, and it denies that humans are 'in it together' on the other hand.
(It denies co-inherence - mutual in-dwelling.)
Christianity places free will and the choice of the individual at the centre of salvation, yet the individual is not isolated but a part of Man, and men are united with each other, and with God by and via Christ.
Our personal choices therefore affects everybody; other people's personal choices affect us.
Good deeds do Good; but evil deeds do evil.
Not merely materially, which is obvious, but transcendentally - in a supernatural way.
When a mass of people in a society are devoutly Christian, this aids the others in salvation; but when a mass of people in a society are consumed by pride and are willing servants of evil - this harms the chance of salvation of others.
When many people in a society have made bad choices, have chosen pride rather than the Lordship of Christ, this is not merely a matter of numerous isolated choices, but an accumulating burden of sin.
This burden is not only felt at the level of a society of interacting humans, although it is felt very directly there, but everywhere in the world, and indeed everywhere in the universe.
Some societies are therefore better than others, some societies are worse than others - human choice makes a difference and not just to the person making the choice.
In some societies salvation therefore is 'easier', more probable, can reach a higher level of sanctity due to the help of others - however, the flip-side is that in other societies salvation is harder due to the effectiveness and ubiquity of temptations (to selfishness, to pride, caused by the choices of other humans) and because the individual would-be-Christian gets little help from others but instead gets misleading advice, deceptions and distractions.
The Biblical prophecies imply that the burden of sin is accumulative through human history, because the consequences of bad choices cannot be cleansed from this world (at least, not without destroying human choice); and that at some point therefore the world will be brought to an end - probably when the probability of any individual choosing salvation has dwindled to zero or close to zero.
In a sense, none of this is any of our business - certainly it is not necessary knowledge, either way we must make the best choices we can in the situation in which we find ourselves.
But - to deny the differences in Christian devoutness in different times and places and types of society is false: it is to damage one's discernment of Good from evil and may be a denial of the co-inherence of each with all.