Who would be dumb enough to spend 2m coins for 1 gem when it's 10 gems to get 1.2-1.9m? What you're failing to see is the possibility of helping those who can't spend money get a better competing edge. For those who can spend, a very small handout of gems wont contribute much. I know this because 1k gems doesn't do much in the way of upgrading my char. A much higher volume of gems will be needed and thus purchasing will continue. You're probably looking at around 2-10 gems being available for purchase every 2-5 days which isn't going to do much on exploiting.