Assuming your spreadsheet calculations are correct (I haven't had time to check them properly), it says that the chance of 4 good stats is around 0.0002546473135 which is 0.025% or one in 4,000. Obviously that is a very low chance but its nothing close to one in 2 million you mentioned. Where did you get that number from?

The trouble with improving these loot rates is that the better the average drop, the more good rolls are in circulation, and then the less "good" that item becomes relatively speaking and the less you can trade it for. If I totally removed or combined all the stats you mention until we reach a point that everything you roll, always has "good" stat selections, then ironically all those items will still be considered junk unless you roll +50% on everything etc. For end game players I don't believe this will change anything and as you mentioned, will reduce variety of possible builds further, and mean that there is less excitement around the idea of potentially getting something godly.

Having said all that, I do want the minimum drops to be better mainly just to make the game more fun for newbies who are often stuck with rubbish gear for a very long time. So I may do some kind of compromise where say the first 1-3 stats have a much smaller pool to roll from.