I think I agree with the game getting fast real quick, especially if your PC has issues handling this - I am hoping the current difficulty will be considered HARD if we get to choose, and I would prefer it being a bit easier - less increase in customer time reducing, slightly lower gaps between the materials, or maybe even allowing to mine Tin with Copper, possibly with really bad gain like ... max 1-2 yield per vein...
However I understand that balancing this is immensely hard without offering a difficulty, because you will always have people bickering about it either being too easy or too hard xD