Evolution-wise, ‘survival of the fittest’ denotes lack of adequate comprehension.
Evolution is about survival. Coping with change. Getting through the ‘dire straits’.
Evolution is free. The only thing that matters is to get through. Nothing else but getting through in one piece.
No referee other than the dire straits themselves and no points for the artistic impression.
‘Survival of the fittest’ is ‘getting through in certain conditions’. Getting through after knocking down all competition…
Survival of the fittest is not about coping with change.
Survival of the fittest has nothing to do with evolution and everything to do with winning.
Ernst Mayr, What Evolution Is

History-wise, Cortes’ religion was better than that sported by the Mexica. Which was good enough – as in ‘fittest’ – for the given conditions, inside the Aztec empire, but unable to withstand being challenged from the outside.

‘Now, will you make up your mind? Is there a best religion or not?!?’

Is there a better DNA? Or a better religion?
Better against which benchmark?

Exactly!

DNA is how species translate information from one generation to the next one.
Religion is how cultural species translate, and conserve, Weltanschauung.

Of course there are differences. But I’m more interested in the similarities present.

We have discovered DNA, and genetics, a couple of generations ago. Evolution, as a process, in the XIX-th century.
Yet animal husbandry and plant breeding are as old as agriculture…
Which means that in certain conditions – having reached a certain ‘maturity’ – humans have started to behave ‘as if’.
Our ancestors, lacking any formal knowledge regarding genetics or evolution, somehow managed to breed a variety of farm animals and plant crops. Each adapted, as in bred to fulfill certain needs, to the ‘task at hand’.

DNA/RNA, the existence of genes, supports all life forms. Plants, animals, fungi, viruses and everything else that lives. As far as we know, there is no life form outside the ‘genetic’ realm. There are many forms of life and all of them work according to the same principle. Each species functions in a specific manner, which manner is transmitted from one generation to the other. The relevant information ‘written down’, encoded, in genetic messages is passed from parents to off-springs.
Evolution, the phenomenon, is a consequence, not a goal.
The messages passed from one generation to the next one are not ‘rigid copies’ of the previous ones. When the messages are put together by the previous generation alterations occur inexorably. Whenever an alteration, or a combination thereof, is incompatible with life, the organism sporting that alteration dies. The alteration disappears.
If the individual organism survives, and is able to generate a new generation, the alteration also survives. And may come in handy when something changes in the environment. Or may prove to be too burdensome in certain circumstances.
Individuals sporting certain alterations have better chances to survive in circumstances where the alterations are useful while the ‘normal’, unadulterated, individuals might struggle. Alternatively, alterations which may have survived for a number of generations might become too burdensome after something had changed.
The point being that evolution occurs ‘outside’. None of the individuals has anything to say about the matter.

‘But you just said that animal breeders have altered their farm animals according to their wishes!’

Yes, the animal breeders have influenced the evolution of their animals! The animals themselves, the individual organisms suffering the process of evolution, still had nothing to say about what was happening to them.

Which brings us to religion.
Information being transmitted from one generation of people to the next one and fundamentally shaping the fate of the community. Of the cultural species being defined by each religion.

And this is where the parallel between DNA/genetics and religion stops.

We don’t know for sure what was going on in our past.
Historians and archeologists have a few ideas but those ideas change as more and more information is literally dug out.
But no matter how much we’ll be able to learn in the future about our history it is safe to say that we’ll never know exactly how we got here. In the present.
But it’s also safe to say that the past was different.

And the most obvious difference being the fact that community mattered more.
In the sense that each and every member of the community was acutely aware of the fact that they could not survive alone.
Each and everyone of the adults living a few thousand years ago were vastly more capable than any of us to survive, for a while, in the ‘bush’. Yet all the evidence we’ve gathered so far suggest they lived in close knit communities.

Absence of proof is no proof of absence?
The fact that “all the evidence we’ve gathered so far suggest they lived in close knit communities” doesn’t mean there were no individuals who managed to survive for long periods of time on their own. Or in small groups.
No, it doesn’t!
The fact that “all the evidence we’ve gathered so far suggest they lived in close knit communities” only suggests, strongly, that close knit communities are more likely to survive. And to leave behind discoverable traces of their existence!