I think the overwhelming majority of Christians fit into the "the two mutually contradictory creation stories in Genesis could not be taken literally even if they didn't contradict each other" camp that I'm most familiar with, or, at most, are nearer the "could be billions of years" end of your spectrum.
edit: after a little Googling, it looks like 51% of US Christians accept a "but it was God's idea" version of evolution, i.e., evolution is how it works, God set evolution in motion. and we probably all know that the US is the only technologically advanced nation with such a high percentage of evolution skeptics. but if it's about all Christians, worldwide, evolution skeptics could be the majority, given that technologically non-advanced countries may contain the majority of the world's Christians.
The features built on top of DNA, however, were built under environments much closer to "peacetime" than "wartime." (Well, maybe not all of them—the "keeping out parasites" logic is also pretty core. But once you can do that, and especially once you have cells specialized for that role in amongst a multicellular body, the other cells can start to evolve some pretty "bureaucratic" notions about how to do things that would never fly if they were directly exposed to a hazardous, resource-scarce environment.)
Maybe the “codebase” was simpler at the time. But it worked far worse. A good software analogy might be today’s Word vs the first notepad.
When you haven't yet evolved adaptations like "strong cell walls" or "the ability to recognize and excrete substances antithetical to your metabolic processes" or "the ability to store metabolic energy for times of resource scarcity", you have to spend a lot more of your time as an organism either moving away from danger, or reproducing away from danger.
And, in environments that cycle between resource-rich and resource-poor, the "reproducing away from danger" strategy is highly preferred: you can always shoot off a germ cell specialized to survive under such resource-poor conditions—i.e. a spore—until it enters a richer/safer environment; and so, when you're in a rich/safe environment, it pays off to have another morphogenic stage specialized toward "thriving" rather than "surviving." (If you're wondering why you'd do this rather than just "turn into" a spore, and then "turn back into" an adult organism, like some bacteria essentially do when dried out—well, that turns out to require more genetic code, especially when you're already doing mitosis anyway.)
2. Things that didn't have robust reproduction mechanisms couldn't evolve these other complex adaptations (cell walls, homeostasis, etc.), because every reproductive step would introduce too many errors for the adaptive "signal" to survive well-enough to spread through the population.
Before any other adaptation, the most important and urgent adaptation an organism that relies upon reproduction can evolve is to increase the robustness of its copying logic to the point that other traits can be constructed cheaply, through focused, linear adaptation rather than random chance.
Or: the probability of any random complex adaptation evolving without DNA is very low. That includes DNA itself, of course. But the probability of any random complex adaptation evolving given DNA is much higher. So you'd expect that, of all the evolutionary lines that survived, they all ended up adapting to use DNA first—because the ones that did some other adaptation first would still have to also evolve DNA [through random chance] to preserve that adaptation for any useful number of generations. Organisms with DNA will strictly outcompete those without, because DNA makes you able to get to any other adaptation much faster—and keep it once you have it, and build on it with further adaptations, until you've got a complex feature.
I would be careful with that example, before you start to sound suspiciously creationist. At least, the Christians I know that deny evolution tend claim everything was created perfectly and since has only slowly degenerated over time.