The 'Production Beeline' is a simply lousy way to design a game. The result is that any new city not within the radius of the Industrial District of an older city can't build diddly/squat from the early mid-game on. In every game, any city I start in the Medieval or later Eras takes 60+ turns to build its first unit and 30 - 40 turns to build its first city center building. What the effect is, is to inhibit expansion of a Civ - again. Since the rising costs of Districts and Builders already inhibit mid-game expansion, this is really a case of stomping on a player when he's down.
What needs to happen is that the Production Improvements/Increases need to be moved to the Industrial Era when they actually started to occur (power tools, steam-driven equipment), production costs reduced for Buildings and some units (but NOT Wonders, which should require some concentration of resources to build) and perhaps the costs of basic buildings (Granary, Monument) should actually go down as Tech progresses. Modern power tools and machinery can whip together a warehouse in weeks compared to older methods of laying brick by hand. Perhaps some very specific Techs or Tech Effects that decrease the cost along about the Industrial Era?