If one prominent evolutionary theory of reason's likely functional role (ie. it developed for justification & persuasion, not primarily decision making) is corr

If one prominent evolutionary theory of reason's likely functional role (ie. it developed for justification & persuasion, not primarily decision making) is correct, then your judgement of 20thC philosophy's significance could be something of a tautology. My impression (from undergrad & postgrad philosophy) was not far off - much philosophy is grounded in sincere attempts to clarify issues of importance, but it's largely doomed to failure (as are scientific attempts to take over canonical 'philosophical' problems - just witness neuroscience's often hilarious tilts at consciousness). That's too long an argument to justify here, but suffice it to say philosophy is truly excellent at revealing our limitations. Which strikes me as no bad thing for a species (and indeed era) whose primary motif could reasonably be considered to be the Dunning–Kruger effect.