Thalassicus
Bytes and Nibblers
One thing to consider is a mined hill gives 4 while a lumbermilled forest gives 1 3 until Steam Power, which is a relatively late tech. Production is scare in this game, so it leaves mines at an advantage for pure production purposes in the first half of the game. Forests can also be chopped for immediate production, and early-game gains amplify to late-game advantages exponentially, which means you have an opportunity cost involved in leaving them as lumbermills.
In addition, mines are used to hook up most strategic resources and gold/silver/gems, so the benefit extends beyond just the features these two improvements can be built on.
There's also the advantages described above of having the bonus at Engineering, increasing the value of that path on the tech tree compared to alternatives. I agree Dynamite is a logical place for a mine bonus from realism, but is already a very powerful tech many beeline to as it gives Artillery, and probably doesn't need a further buff. An alternative might be to make Steam Power boost production on both tiles, instead of only on lumbermills. Or, putting a mine bonus on Railroads, a traditional place for that.
In addition, mines are used to hook up most strategic resources and gold/silver/gems, so the benefit extends beyond just the features these two improvements can be built on.
There's also the advantages described above of having the bonus at Engineering, increasing the value of that path on the tech tree compared to alternatives. I agree Dynamite is a logical place for a mine bonus from realism, but is already a very powerful tech many beeline to as it gives Artillery, and probably doesn't need a further buff. An alternative might be to make Steam Power boost production on both tiles, instead of only on lumbermills. Or, putting a mine bonus on Railroads, a traditional place for that.