Is it a waste of time for most, to invest into these sort of posts, because Conscientiousness is rigid?

I think you should first ask, what is meant, statistically, by the results we're describing as 'rigid'. If ~50% of population variance is genetically linked, what does that mean in practice?

Second, one should then ask, is there such a thing as 'being efficient with Conscientiousness'? Somewhat like willpower - are there better or worse ways of deploying willpower? What would this even mean?