@bulliednoob One of the biggest complaints I've received over the years is that tournaments last too long, so I when I design tournament formats I try to optimize for tournament speed while preserving competitiveness. If I did a BO3 that was in the order of 20km -> 10km -> 5km, I'd expect it would add on average about 10 minutes to each BO3 round, adding about 30-40 minutes to overall runtime. Considering that this format can run between 6 to 7 hours already, I'm not inclined to do anything to extend that length.
I also do not think the current order favors players who do better on small maps in a significant way. If you are going to win the BO3 you still need to win 2/3 map sizes, no matter what order they are played in. I'd argue the fact that the loser's bracket contains about half 10x10s and half 20x20s with no 5x5s favors players who are better at big maps in a much more significant way.