1-2 years of research? Take for example the iPhone 15. What’s so different from the 14, 13, 12 except from camera upgrades (not developed by Apple)??? Same for iPad and Mac. How long did it took them to develop a new Mac Pro? Most brands would go out of business by this pace.This is normal. Every Apple hardware device that we buy was in development for at least 1-2 years. Design, development, testing, suppliers, manufacturing, packaging, support resources... it all takes time to execute.
Apple is not starting the next iPhome in October the month after they announce in September. The next iPhone (two Septembers from now) is already under development today.
The rumor mill is just getting better at tracking these hidden details.