For one, "insane micro" was around before SC2 and was more of a deciding factor in BW than SC2. For instance, if you pay attention and analyze pro games you'll notice that macro (the boring repetitive work) that you think was flushed out from BW was actually just translated into other, equally monotonous tasks in SC2. Also, SC2's fights (outside of early skirmishes) are MUCH more based around creating concaves or fighting in favorable positions, and not actual micro. In BW micro is far more of a deciding factor in fights. (see: any pro-game fight consisting of supply over approximately 120 aka deathball)
Another thing, MarineKingPrime didn't really "invent" marine micro, he just excelled at it. And SlayerS isn't a player, it's a team name.
For the last part regarding optimal resource management and exploring timings and makeups, build orders have been virtually completely fleshed out and maximized. There really isn't much that say, 1000 APM (just a stupidly high impossible number to represent computer APM) could do that 300 APM (pro player human APM) couldn't in terms of gaining an early advantage in build orders.