The vanilla "arable land" system resolves around the starting population. More pops = more arable land and vice versa. Thus mainland China has lots of arable land and e.g. Patagonia has few. This system works well in general, but not when it comes to the lands quite arable yet not densely populated in the year 1836 (such as Great Plains, or even South America itself).

There's also a problem with ahistorical resources distribution — somewhere deposits are too few, somewhere are too much. And the current distribution itself generally makes the resources more accessible and less rarely encountered around the world, I feel. There's just no point in colonizing Africa when you can conquer your neighbour and get precious <resource_name>.

But one dude already came up with a solution to both of these problems — look at this mod. He reworked the whole "arable land" system together with resources distribution, making them closer to historical values at those times.

I guess its integration would greatly benefit the mod while not downgrading any performance — yet improving realism and increasing general strive for resources (causing real imperialism and need for colonization). The integration process itself shouldn't be too hard either — I even saw someone's own submod which integrates it into Great Rework. It's just a matter of a few new provinces added in Great Rework which need to be handled.