... The two examples are utterly subjective and I suspect you can ask 100 people which the[y] prefer and you'll get different answers from the group. Either is acceptable visually to me...
Ok, "prefer" is indeed subjective. And "acceptable" isn't really a high praise.
But let's rephrase the question. Let's ask 100 people which of the two they are more likely to use the following words to describe: dull, lifeless, flat. I am the first one to attached them to the first waterfall image. The OP does as well. I bet the majority of the 100 would do so.
And that really is the question the OP is asking since post #1: why are raw files generally perceived as more dull and flat, compared to adjusted files or even the out-of-camera jpegs.
My uneducated guess would be that raw files do not know which way users would like to go in post, so they offer a middle-of-the-road starting point, neither here nor there. If I may use an analogy, it is like a supermodel's picture in the morning, right out of bed, compared with the one after hours of makeup and hair styling. Now, of course, various people might prefer the natural look, but if asked which look would be more likely described as Plain Jane and which of a supermodel, the answers would be more unified.