Now I’m thinking economic victory is so fast when playing for it (expanding or trading for 40+ factory resources) that it dooms factory resources to feel least impactful in many games when you have the most of them. Since you just click next turn to victory.
They sure boost science and culture visibly, directly and through growing more specialists, so I guess they help shrink more gameplay into fewer turns. In those 25-30 turns I suppose you could have an entire world war (or two) trying to unseat each other victory contender.
Edit: distracted myself, what I was going to add was this might be one way a fourth age could shine, is letting factory benefits last longer and have more of an impact. However, keeping the game interesting into a fourth seems so far beyond reach.