If we define improvement as a function of where we were vs where we are now then it doesn't really mean much. What we really need to look at is how much we have improved in comparison with how much other teams have improved.
For example lets say 10 years ago we struggled to score 200 in ODIs and now we can consistently score 250. Does that mean we have improved? NO! because back then 250 was a per score in ODI and now 300 is a per score for the rest of the world! So actually after 10 years we are still 50 runs behind the per score.
Rise Against Tyranny