Diagnose it in Search Console rather than by intuition: filter by query, look at which URLs receive impressions for it, and watch for a position that oscillates as the engine alternates between two candidates. That oscillation is the tell, and it usually costs more traffic than either page's absolute position suggests.
The fix is consolidation, not optimisation. Merge the better parts into the strongest page, redirect the weaker URL to it, and update the internal links that pointed at the retired version. Publishing a third page on the same intent, which is the reflex, makes the problem worse.