So the question is this: why, or how, could information (DNA) and an interpreter (RNA) conveniently arise at the same time so that they can be useful to one another?
That's kinda like asking how a car's engine and fan could arise at the same time. The engine is needed to turn the fan and the fan is needed to cool the engine. You're saying that neither would work without the other.
The answer, of course, is that they both existed before they came together in one system. Fans were used for ventilating mines and engines were cooled by convection. They both had other uses and were independent of each other.
Life is like a Hot Wheels car. Sometimes it goes behind the couch and you can't find it.
And before DNA and RNA were brought together in one system, DNA was used for....? And RNA was used for....?
It doesn't matter what they were "used for". The point that negates your argument is the fact that they could both exist and have the same chemical behaviour as they do now but without "working together". The parts of a system do not have to develop at the same time.Life is like a Hot Wheels car. Sometimes it goes behind the couch and you can't find it.