With all due respect, why would you have even upgraded to begin with?
I had a first-gen 12.9 Pro....So the upgrade for me was huge. But let's be honest - There are very few gadgets where you are going to see an initial leap in difference going from just one year to the next. That's why most people only upgrade every 3-5 years or perhaps even longer. Apple (and other companies) always have to balance their new tech and feature-set with the fact that most people will always be running older hardware. So it always comes down to a balance of what "cool new stuff" you can offer up, countered with making sure that the majority of people can still enjoy it.