I am also unconvinced that ECI is a better metric to use than AAII. One issue with ECI scores is that they are often calculated using just 2 benchmark scores for a particular model
We use a minimum of 4 benchmark scores, not sure where the 2 is coming from?
IMO this is a potentially significant issue that this post should have spent more time addressing, since it means that the earlier sections of the trend lines are coming from a source we know nothing about.