Boris Gudenuf
Deity
The Iron Relevance problem is two-fold:
Making the Iron-dependant units meaningful (Swordsmen)
Making Iron more generally useful later in the game
Making Swordsmen more useful doesn't require buffing the Swordsmen, just giving the other units their Historical Penalties:
Pikemen: get a -33% modifier on Hill, Forest, Jungle, or Marsh tile
Catapults, Trebuchets: -50% against Units of any kind
That makes the Siege Weapons strictly city attackers, and makes Pikemen very vulnerable to the more maneuverable swordsmen in any kind of rough terrain - which was historically true.
Next, Iron is not required for cannon. Most of the early cannon were made of Bronze or Brass, and (wrought) Iron was only used for heavy siege mortars and naval guns (so it is correct to require Iron for Frigates, Ships of the Line, and Ironclads)
The massive use of Iron is for Railroads - you cannot build them without 1000s of tons of the stuff. Thus, even if you can squeak by without it in the Classical and Renaissance Eras, (be friendly, keep your head down) you will need it in the Industrial Era - but by then you've had a bunch of turns to find some sources.
Making the Iron-dependant units meaningful (Swordsmen)
Making Iron more generally useful later in the game
Making Swordsmen more useful doesn't require buffing the Swordsmen, just giving the other units their Historical Penalties:
Pikemen: get a -33% modifier on Hill, Forest, Jungle, or Marsh tile
Catapults, Trebuchets: -50% against Units of any kind
That makes the Siege Weapons strictly city attackers, and makes Pikemen very vulnerable to the more maneuverable swordsmen in any kind of rough terrain - which was historically true.
Next, Iron is not required for cannon. Most of the early cannon were made of Bronze or Brass, and (wrought) Iron was only used for heavy siege mortars and naval guns (so it is correct to require Iron for Frigates, Ships of the Line, and Ironclads)
The massive use of Iron is for Railroads - you cannot build them without 1000s of tons of the stuff. Thus, even if you can squeak by without it in the Classical and Renaissance Eras, (be friendly, keep your head down) you will need it in the Industrial Era - but by then you've had a bunch of turns to find some sources.