Seems that something like your suggestion would be (even) better than the current ranking system.
My iterative suggestion is to perhaps average the middle half of your matches... I think this would probably be even more accurate to teams' capabilities throughout the rankings. My suspicion is that this year's rankings work phenomenally well in events where:
- # of matches to # of teams ratio is high
- Most teams aren't improving dramatically
- No teams have 'outlier-like' performance
but probably become weaker, particularly in the middle and lower ranks, when there are more teams, fewer matches, and 1 or 2 powerhouses. Since a powerhouse can put up so many points, you'll see teams that would have a QA of 50 get bumped up to 60, just by playing a single match with a team that puts up 150pts. Particularly in the upper-middle section of the rankings, having a terrible match can drop you like a stone... this would also assist with that scenario.
So my recommendation is to take the middle 50% of your match scores.... average all those together. This nearly eliminates the impact of having 1 or 2 fiercely unlucky (or lucky) matches, but will still reward the 'consistent performers' who are just very good every time they go out there.