You're always going to see that with any mature market product. TV's, cars, houses, etc don't see huge leaps, they see incremental ones. The new 2019 Ferrari an iteration and incremental one on top of the 2018, rather than a giant step forward. That's normal.
It's more about coming to understand that. Once you do, it's not a disappointment at all. You realize that now it's more about making smaller changes that add up to larger improvements in our daily use. If those advantages add up enough to justify it, you may want to upgrade. I know they make it well worth it to me each year (the added productivity pays for itself quickly). If they don't, don't upgrade as frequently. You won't feel as left behind and save yourself some money. Nothing wrong with going either way.