The big diagram is contingent

Yup. Is that supposed to make it not a counterexample, and if so why? (Note that, e.g., the processes affecting mood, tiredness, etc., are also contingent. You may wish to avoid stipulations that make my counterexample not a counterexample if they also make your leading example not an example :-).)

Again, I'm not disagreeing that many good ideas are simple and that simple ideas are worth pursuing even if you expect that they're never going to be more than useful approximations that may point in helpful directions.

And most neglected of all: Purpose.

My feeling is that if "purpose" is neglected in science it's because it's generally been found to be more misleading than helpful. We can ask, in evolutionary mode, "what if anything gave this a selective advantage?" or, relatedly, "why didn't this costly thing get selected out of existence?". And we can ask "what does this actually do?". What does talk of purpose add beyond these?

It adds something in cases where some actually purposeful agent is responsible for whatever-it-is. So, e.g., I expect it's useful from time to time in finance where the answer to "why do these prices move in this way?" may be "because the owners of these pension funds have these incentives and are acting accordingly", and it's certainly useful in politics or history. But in biology? It seems to me that if you find cases where the full-blown concept of purpose is genuinely better than the alternatives, you've found good evidence[1] for creationism, and so far alleged cases of good evidence for creationism have tended to evaporate on closer inspection.

[1] Of course good evidence is not necessarily anything like proof; sometimes there is good evidence for false things.